Kalkwasser and Specific Gravity – 02/04/08
Hi, WWM Crew.
<<Hiya Al>>
Great site and thanks for all the past help.
<<Glad we could be of assistance>>
I have a question regarding salinity, specific gravity and Kalkwasser.
<<Okay>>
I dose Kalkwasser through my auto top-off in to a 180g reef tank with a 50g sump. My evaporation rates are fairly large and I was wondering what effect Kalkwasser had on my specific gravity reading.
<<Nothing of significance>>
Specifically (no pun intended), could an abundance of added Kalkwasser contribute to an increased level of specific gravity?
<<Not as I am aware. I have heard before some hobbyists reported “small” increases in Salinity with the use of Kalkwasser…but I haven’t seen any scientific claims re, nor have I experienced this with my own tank (that I could tell, anyway). I think some of these “reports” may well stem from the use of commercial “two-part” Calcium and Alkalinity supplements as these do impart both Sodium and Chloride ions to the system which would contribute to an increase in Salinity over time. But all in all, even with such additions, the increase in Salinity should be very gradual and easily managed through normal good maintenance/husbandry practices>>
Thanks again!
Al
Lake Tahoe, NV
<<A pleasure to share. EricR…Columbia, SC>><Specific gravity increases with any solubilized solid material... RMF>

Re: Unintentionally Kill New Finger Leather?, & Spg measure...  12/25/07
Thanks a bunch Bob!
<Daryl>
I thought you would like to hear some good news...
<Always>
The "finger leather" is still alive... and is beginning to extend its polyps! (see Finger Leather.JPG). Also, the "kenya tree coral" (?) has shed all its mucous and looks just great! (see Kenya Tree Coral.JPG).
I've already noticed a reduction in algae after switching to RO/DI, adding a Turboflotor skimmer, and adding a Yellow Tang! Everyone seems to be doing great! My coralline algae is starting to peal and turn pale in spots... I suspect replacing the light bulbs and the glass covering over the tank has something to do with it.
<Likely so>
Also, just a quick question regarding specific gravity/salinity. I have a plastic, swing-arm type hydrometer (Deep Six Hydrometer). It is stated that it gives temperature-corrected readings in warm water aquariums. The hydrometer shows a bracket (which I assume they are marking 'normal readings') between 1.020 (~27 ppt) and 1.023 (~31 ppt). I am under the assumption that I should have a specific gravity of 1.024 (~33 ppt)??? I've also read that natural seawater is around 35 ppt (~1.026). I think I'm making this a bit too confusing... basically, what should I be reading on my Deep Six Hydrometer?
<About 1.026>
Also, my pH is around 8.2 (two hours before lights out). I would like Is there a way to increase the pH without affecting the alkalinity?
<Posted... Read here: http://wetwebmedia.com/marine/maintenance/index.htm
scroll down...>
Water Specs:
Salinity 33 ppt
Temp 78
pH 8.2
Nitrate 0
Ca 430
Alkalinity 3.5 mEq/L
Mg 1500
Thanks for all that you have done. I hope you had a very Merry Christmas!
Also, when is your 'reef book' coming out?
Daryl
<I wish someday soon... no scheduled production time... but I do keep bugging JamesL, my US publisher re... Cheers, Bob Fenner>

Refractometer 07/27/07
Hi Crew
I have a quick question if I could bug you guys again. I bought a refractometer after reading some of your posts about hyposalinity. Just in case I need to use it for ich in the future. My refractometer is off quite a bit compared to the swing arm hydrometers I have. I have 2 deep six by CoraLife hydrometers and a SeaTest hydrometer. All 3 tell me my SG is 1.020 and my new fancy dancey refractometer is telling me my SG is 1.024. Big difference. I calibrated it as per directed. I checked seawater from the Gulf Of Mexico off the west side of Florida and the refractometer tells me the gulf is 1.030 SG. Is that normal SG for the ocean or would you say my refractometer is off? I checked the gulf water with my 3 swing arm hydrometers and they are almost at 1.024 just a tad under. The funny thing is I bought this much more expensive refractometer to be more precise and I think my swing arm are more accurate. Anyway to calibrate it I was wondering if you knew what the Gulf Of Mexico SG is?
<Probably somewhere around 1.027. However, you should probably account for a possible/likely rise in salinity due to evaporation during the trip from the gulf to wherever you are.>
I did a google search and couldn't find anything? Also for what its worth the refractometer I bought is temperature self adjusting. Thanks In Advance.
<I would trust your refractometer over your hydrometers (especially if you recently calibrated your refractometer. In fact, hydrometers are usually calibrated against refractometers.
Best,
Sara M.>

Re: Refractometer 10/28/07
Thanks so much for your fast response! There was no evaporation because I checked it right at the gulf shore. 1.030 every time.
<Oh, huh...>
What I was going to do is use gulf water and then calibrate at 1.027. I thought 1.030 was way to high. Maybe its a cheap one I bought?
<Well, how cheap was it? Did you pay in quarters and have to turn a knob until it came out the bottom of a machine? :-) j/k The "cheap" ones usually work fine. I think it just needs to be calibrated. But I wouldn't use water from the gulf since we don't know exactly what that salinity is (my guess is it could be anywhere from 34 to 36 ppm). Instead, make your own standard solutions and calibrate it to those. See here:
http://www.reefkeeping.com/issues/2004-06/rhf/index.php>
Looks nice but isn't 1.030 way to high? Thanks you guys and girls are great!
<De nada and good luck,
Sara M.>
<I'm so sorry, in that last response I meant to type "34 to 36 ppt" NOT ppm. -Sara>

Specific Gravity Question  10/11/07
Hi Neale! I've been studying up on my next adventure - a marine tank (30-55 gallon) - namely with clownfish. I realize specific gravity measurement is important however in all the research I've done, I can't seem to locate HOW to measure specific gravity. There isn't a test kit for this is there?
Relates to salinity doesn't it?
<Hello Lisa. You need to use either an hydrometer or a refractometer. Or if you have the $$$, an electronic salinity meter. There's plenty about them here: http://www.wetwebmedia.com/spg_salinity.htm . I'd also add that a marine aquarium should be a mandatory purchase before going into marine fishkeeping. While you can sort of "pick things up as you go along" with freshwater fish, for marine fishkeeping you do need to hit the floor running. Bob Fenner's book 'Conscientious Marine Aquarist' is superb, and I'd say that even if the guy was a schmuck. As it is, Bob's a nice guy too. On the front page of the web site there's a deal right now for two of his books for a measly $30. Definitely worth considering, and given the price of even a single marine fish or coral, learning from someone like Bob will save you hundreds of dollars in the long run (not to mention the lives of those gorgeous sea creatures) -- http://www.wetwebmedia.com/daily_faqs3.htm? . Otherwise, browse, read the many articles on marine fishkeeping here at WWM.>
On another note - is it possible for 2 year old livestock to grow when brought into a more spacious environment? (i.e. Mbuna, Plecos)
<Yes and no. All fish grow constantly. This is actually standard for "lower" vertebrates. It's called non-determinate growth. It contrasts with birds and mammals, which grow to a certain size, and then stop. Anyway, what changes with fish is the rate of growth. This is normally fastest during the early stages of growth. In the case of a typical tropical fish, this will the first few months. Growth rate then slows down, to the point where after a few years growth is imperceptibly slow. The bottom line is that if a fish has been "stunted" in its first year or two, it is unlikely to ever reach the maximum size for that species, even if moved into ideal conditions. It's passed through the rapid growth phase, and all that's left is slow growth. In other words, yes, your Mbuna or Pleco will grow bigger in a new tank, but don't expect them to get *as big* as ones that had been in a bigger tank right from the start.>
Thank you and I look forward to hearing from you!
Lisa
<Hope this helps, Neale>

Re: SG Problems... measure, refractometers   7/21/07
All I can say Bob is wow! Since sending you this e-mail I have been on a roller coaster ride of specific gravity instruments and their calibrations.
I feel like I have learned a lot and thought I should report back to let you know what I came across (since this gets posted and all)
<Do appreciate this>
Okay, so in the beginning I put some straight RO on my refractometer and it registered as about a half an inch below where the scale even started.
That's .5" below the 0 line on the instrument. This is what lead me to freak out and write you because once I dialed it up to 0 my salinity read 1.029 which had me near panic as at that time I thought it had likely been that high for months. Since then I began digging on the forums and found that with the decline in price on refractometers, the quality of the instruments has also been in decline. Basically the cheap ones (which I have) become unreliable the further the reading gets from the calibration point so it is much better to calibrate with a solution at 1.026 than it is to calibrate it with fresh RO at 0. Thanks to Randy Farley on Reef Central I found a homebrew calibration solution that was extremely simple to make, once I recalibrated my instrument using this solution, it turns out that my 1.029 water is actually at 1.022!!! and likely has been for all these months because of a bad refractometer calibration with straight RO. This 1.022 reading has since been triple checked against another refractometer, a conductivity meter, and a swing arm.
Basically I wanted to write you back so that when this is posted, hopefully some people catch it and realize that they need to rethink how they are calibrating these instruments and not blindly trusting them like I did. I am now using my fresh saltwater for my auto top off to slowly bring the salinity up to 1.026 and feel as though I have been on a roller coaster ride thru a salinity nightmare. Anyhow, cheers to you guys and I really hope this helps at least one other person. Now that I have this behind me I am off to have a margarita.... hold the salt.
<Heeee! Thanks Bush. BobF>
Bush Williams
PS, here are the links I was talking about:
Calibration discussion:
http://www.reefcentral.com/forums/showthread.php?s=&threadid=953605
Homemade Calibration Solutions:
http://www.reefkeeping.com/issues/2004-06/rhf/index.php

Hydrometer Inaccuracies 4/20/07
What is the best way to measure salinity? <A refractometer.> I bought a normal plastic Instant Ocean pendulum hydrometer but when I test my SG it will measure about .002-.003 difference when I take a water sample to my LFS. <These are pretty unreliable.> They use the exact same hydrometer I use. Do I need to calibrate it and if so how do I do it?  <They can't be calibrated.  Best to make sure that the water temperature is close as possible to what the hydrometer wants and there are no bubbles on the swing arm.  My advice is to invest in a decent refractometer, much more accurate and easy to use.>
<Chris>

Refractometers
hi guys:)
<Hello...Jorie here>
Quick question,
I have 3 hydrometers and get a different reading off each and am fed up. I want a refractometer and don't mind paying the extra buck for quality.  I was wondering if you would feel comfortable with a refractometer from 1 one of the fallowing manufactures. Ocean Tech, Vital Sine,  Captive Purity.
Which would you pick? Do you have a better choice perhaps?
ocean tech, vital sine   http://www.drsfostersmith.com
captive purity:  http://marinedepot.com   
<I purchased the following refractometer about a year or so ago and absolutely love it.  Knock on wood, have had no problems whatsoever and would without hesitation recommend it to anyone in the aquarium hobby.  No need to pay the "big bucks" for all the bells and whistles unless you are a chemist, in my humble opinion!
http://www.reefaquariumguide.com/sponsors/specials.php
many thanks
<You are most welcome.  Take care, Jorie>

Pinpoint Salinity Monitor Problems 2/18/06
Hi gang,  I've run a Pinpoint ph monitor on my reef system for several years. . . overall I'm pleased with it, although it has to be run with a 9 volt battery. . . two attempts at using the optional adapters provided by the manufacturer went astray -- I had a techno-geek friend test the second one after it shorted out my unit for a while. . . turns out the adapter was supplying 11.8 volts. . . way too high, and almost destroyed the monitor. The salesperson at my usual internet supply source confirmed the adapter unit is cheap/unreliable.
<Indeed, the power supply problem is well known among Pinpoint users, and you would think they would supply a better quality unit, but alas... pinpoint monitors are made to be inexpensive hobbyist models.  Top of the line models cost much more.>
On to my real point. . . a month ago, I ordered a Pinpoint salinity monitor. After calibrating the unit, I added it to my reef tank. Readings were WAY high and fluctuated wildly. I called the supplier. . . who was immediately aware of the 'problem'. Turns out the unit won't function properly in proximity to electrical current. . . e.g. my power compact reef lights. Since the only places available for mounting on my system are a crowded sump with several hundred watts of pumps being powered up (returns and downdraft skimmer pumps) and the top of my reef tank, there's nowhere I can run the relatively short (less than three foot) probe-and-cord to use the unit. I feel like I've effectively purchased a hundred-dollar-plus paperweight. As the last straw, the unit ate up a 9 volt alkaline battery in just a week's worth of use. The thing is, there's no disclaimer describing this problem on the website where I bought the thing. And the supply source wasn't willing to allow me to send back the unit to upgrade for another Pinpoint product. So 'caveat emptor' on this one. . . Chuck
<It is a shame that this problem exists, and pinpoint should probably at least state in the instructions that the unit must be away from such interference, but again, these are entry level inexpensive products.  Your comments are appreciated and will be posted amount the FAQ's.  Best Regards.  AdamC.>

Refractometer Accuracy  1/20/06
Hi WWM, from snowy Nevada!! Hope there is better weather where you are!
<Ah yes. A beautiful day in Georgia.>
I have a refractometer that is approx. five years old. I recently had reason to question the accuracy of the meter, when someone else was testing the same sample water with another refractometer and received a completely different result than my refractometer.  Both refractometers had been calibrated. I purchased another refractometer as did someone else I know. We took all 3 refractometer's and calibrated them at the same time with the same water. Then took some sample aquarium water and tested it with all three. My five year old refractometer tested the water at 1.025, my new refractometer tested it at 1.025, and the third refractometer tested it at 1.022.  Is this a significant difference between meters that should be of concern?
<Not really.>
It seems the results should have been more similar, given that all three were calibrated in the same way, at the same time, with the same water.
<Actually, most are only accurate within the certain temp. planned for their use. Probably what is the case here.>
Another notable tid-bit, both of my refractometers have the same model number RHS-10ATC, and the third has a model number of ZGRS-10ATC. Could this just be the difference in models?
<Yep. Probably meant for best results in certain temps.>
None of the meters list any kind of accuracy reference. Which should we consider more accurate?
<Try to find out the intended temp. for each. As long as you get consistent results from the one you are using, you should be fine.>
I am very curious to hear your thoughts.
<Oh, and I do have some curious ones!>
Thank you very much and have a great night (hopefully in some tropical location)!! Jen Marshall
<Hmm...Tropical? Well, there are some "strange birds" around here! - Josh>

Hydrometer Readings  3/16/06
Hello there, <Hi Czarina - Tim answering your question today!>
We have just set up a new 40 gallon aquarium. It currently contains nothing more than saltwater and live sand (with sump, bioballs, heater set to 77, pump etc). However, EVERY time we test the water with a hydrometer we get a completely different reading. Sometimes the needle hits the very top of the meter, then 3 seconds later the bottom, then somewhere in the middle (not necessarily in any particular order). We went and bought a second hydrometer to double check, and exactly the same thing is happening. We are taking these readings without leaving any time between them- so there is no room for any fluctuation. We have not added salt for a few days either. The guy in our LFS said there is no way this could happen. Also, it seems that when we put it under and hold it there, we get a higher reading it seems- than if we fill it and lift it out quickly. <It could be that you have bubbles stuck to the needle when you first fill it, causing it to jump high, then fall once the bubbles come off. Alternatively the needle could be getting slightly wedged at the bottom. In any case, fill the hydrometer to the recommended level - and ensure that your water is at the appropriate temperature for measurement (should be ca. 25C for most hydrometers but check the instructions supplied by the manufacturer). Then, depending on the model and whether or not possible, place the hydrometer on a level surface - e.g. a table top or similar. Tap the outside of the hydrometer (if it is plastic - not glass) with the tip of a pencil or pen a couple of times to dispel any bubbles in the hydrometer. Then allow the needle to stabilize and you should have an accurate measurement. I think the answer really is down to physics here!>
I am completely and utterly confused as to why this is happening. This crazy
fluctuations can't be possible <Exactly - they can't unless something on the needle is causing this such as an air bubble.>. Please advise us!
Thank you for your time, <Always a pleasure!>
Czarina.

Refractometer vs. Hydrometer question    11/27/06
Dear Crew,
<Dear Eric, Mich here, hello to you on the first day of deer season.>
I have been using a Red Sea Hydrometer for as long as I've been in the hobby which is about a year now. I decided to upgrade to a $60 Hand Held Refractometer w/ATC on sale for $30. <Good investment.>  I calibrated it this morning by setting the room temperature to approx. 68 degrees F. and a couple of drops of distilled water as directed. I then proceeded to test some buckets of pre-made salt water. To my astonishment every bucket was 1.028 SG. I went to my main tank and it was 1.0275, which is probably due to it being 78 degrees. My quarantine tank was the same. My hydrometer has always read 1.0235 consistently. I would do this 3 - 4 times in a row to ensure the result was consistent if not accurate. <As you know consistency and accuracy are two different measurements, both equally important.>  I thought it might be off by .001 but not .0035 - .004.  <Hydrometers are notoriously inaccurate.>
Thankfully all the corals in the tank are doing fine. <Good.>  I only have two fish: a blue/green chromis and a Hippo tang who thinks he's a chromis. The tang has some scarred looking flesh which has been there since a week after I got him. Could this be from too high SG? <Could be may things.>  (it's a grayish color in patches and his tail has looked frayed forever. The cleaner shrimp enjoys picking at him when the fish lets him.) <Good.>  Is it possible that the Refractometer is also off? <Doubtful.>  Should I trust the refractometer <Yes.> and slowly drop back to about 1.025 or 1.024 over the next few weeks during water changes<Yes.>? I think I'll bring a sample of water to the LFS to double check before I do much of anything, <Good...if they use a refractometer.>  but I would like to hear what you have to say. <I would trust the refractometer, not the hydrometer.>  Is it normal for Hydrometers to read low? I've heard they can read high, but not low.  <Hydrometers can be inaccurate in any direction.>
Thanks for your time - Eric <Welcome.>

Measuring Salt Content – 10/25/06
Hi Eric,
<<Hey Ken>>
I finished the tank, filled it up, turned it on, and no leaks.
<<Yea!>>
What a relief.
<<Indeed>>
I want to test the SG in the tank.  I have a Blue Line ( I think) model RHS-10ATC refractometer.  I get a reading of 1.025 on this.  I also tried a Coralife "Deep Six" hydrometer and get between 1.021 and 1.022.  Does this seem normal to have this kind of range?
<<Sure...the plastic box-type hydrometers aren’t consider very accurate, but they are generally close/consistent enough for hobby use and are convenient for “quick” checks, especially if you have something like a properly calibrated refractometer to use for reference.  Personally, I prefer to use an electronic meter for measuring salinity but what you have should be fine>>
Thanks,
Ken
<<Always welcome.  EricR>>

Meniscus...Is It Up Or Down? – 10/12/06
Dear Crew,
<<Hello Eric>>
Thanks for all the help you have given me in the past.
<<Quite welcome>>
I currently use a floating hydrometer/thermometer to measure the specific gravity in my tank and replacement water.
<<Mmm, not very accurate...unless you have spent money for one of the better “lab grade” hydrometers (they generally don’t contain “thermometers”) as offered by Salifert, and pay attention to/have a conversion to allow for water temperature>>
When using such an instrument, I have noticed that there is a reverse meniscus (shaped like a ' n ' instead of a ' u ‘) around it.  Do I read the specific gravity by checking the level of the water surface or where the reverse meniscus reaches?  I know usually a meniscus is read from its base but I have never dealt with a reverse meniscus, if that's what it is called.
<<Hmm, describing the meniscus as either an ‘n’ or a ‘u’ is a matter of interpretation I think.  Regardless, read the hydrometer where the surface of the water just outside the meniscus would strike it>>
Thanks,
Eric
<<Regards, EricR>>

And then there were none... substantial obeisance, hydrometer accuracy, troubleshooting SW illness...  - 09/14/06
Hi,
You guys were a tremendous help to me last time, I went to Amazon and ordered anything with the name Fenner on it. (great books)
A little background on the tank.
I have a 50 gallon saltwater tank, 2 years old. pH normal, Nitrates normal, Nitrites normal, SG 1.022, temp.77-79, Nh3 negative. 30 Lbs live rock, and a 1.5 inch bed of live sand (infested with what I think are bristle worms, little orange things that are grey at the end). The lights run 10 hours a day, and I have a very healthy growth of bubble algae and the like. ( the tang loved it )
In the last three weeks I have lost,,,,  A yellow tang, 2 clowns, 5 assorted damsels, a mandarin (sob!)
<Yikes>
  and a citron goby. I have introduced an anemone, and a feather about two weeks ago, but they seem fine.
<... likely the Anemone is involved, related to your fish losses here>
My crabs and snails are all fine, but I tried to put in cleaner shrimp to help stem the massacre, and they died about 20 minutes after being put into the tank. (do I need to recalibrate my hydrometer?)
<Doubtful... but I would "check" it against a known-to-be more accurate device... and raise your spg to 1.025>
The fish were coated with a grayish mucus especially noticeable on the eyes, I have cultured the water
<Neat!>
and found Gram negative bacteria such as, Proteus, and Pseudomonas.
<Very common "similar" microbial involvement in all marine waters>
The fungal culture will take a bit longer to grow.
I rarely do water changes, but the tank evaporates about 2-3 gallons a week that I refill with RO water. I have a canister filter that the LFS guy says not to touch "if your water is so clear, and the parameters are so good, don't even clean it, you will kill the bacteria that  live there", so I added another smaller canister filter.
<Mmm... am not a big fan of this technology for the vast majority of marine systems. See WWM re>
I don't know what to do, this has happened at the end of last summer as well, and I simply left the tank empty for 6 weeks to crash any parasites that were there, and then added fish and they were fine, but this time I don't think it was parasites.
HELP PLEASE!!
many thanks,
josh
<Well... Please read here: http://www.wetwebmedia.com/anemcompfaqs.htm
and here: http://www.wetwebmedia.com/marine/setup/filtration/marineFiltr.htm
and the linked files above....
And consider adding a protein skimmer if you don't have one, better filtration period, trading in the Anemone... Bob Fenner>

Hydrometers
Hi Bob-
Which hydrometer would you recommend. Aquarium Systems Sea Test or  Coralife Deep Six.
Also should I hard plumb my w/d with the hang on overflow or use the flex hoses?
Thanks
Tom
>>
Six of one, half a dozen... they're about the same... more important in terms of accuracy and care of these measurers of specific gravity is learning how to use them... tapping their boxes to rid air bubbles, rinsing them, and storing them carefully (a zillion dollars worth will be broken today!) especially. These plastic "box type" hydrometers are better than glass types though... and accurate enough for commercial and hobby uses.
Bob Fenner 

Hi Bob,
I have one other question for you.
Is their a formula to convert temp, salinity, to specific gravity?
pH ORP Temp Cond. Sal.
8.13 323 80.2 58700 38.49
8.19 317 79.7 59500 39.06
8.11 320 80.1 60100 39.49
8.14 319 81.4 60100 39.48
8.27 319 80.9 59800 39.27
8.12 316 81.4 60800 39.98
8.05 316 79.8 60200 39.56
8.03 315 79.8 60200 39.56
8.01 316 80.3 60800 39.99
nitrate 0, nitrite0, Amm very little, all most not detected
Alk 5 meg
Cal 425
phos .1
dKH 10
Thanks again,
Larry
>>
Hmm, I'd rather offer a table rather than a formula here... And a warning to not get overly excited about this aspect of water quality... best to "return your water to center, or thereabouts" via water changes on a regular basis, as more than salinity is at play in figuring to or from relative density (specific gravity) or seawater.
Assuming a constant salinity of 34ppt, varying temperature, the spg should read:
Temp.F Temp C Spec. Gravity
86 30 1.021
84 29 1.021
82 28 1.022
81 27 1.022
79 26 1.022
77 25 1.023
75 24 1.023
73 23 1.023
72 22 1.023
70 21 1.024
Bob Fenner

My fish are sick
Thank you for answering my questions. I guess in my efforts to give you all the information you needed, I overlooked one of the most important things.
I do have some test kits I use. The ph level is and has been 8.0 the entire time I have had the aquarium. My nitrites are and have been 0. There aren't traces of ammonia. The only thing that has changed during the time I have had everything are the nitrates. They started at 0 and after about 2 months increased to 20, after about 3 weeks increased to 40, and have stayed at 40 for the last few weeks.
How do I lower my specific gravity? How do I measure it?
<With a tool called a hydrometer... and it can be lowered by removing some of the seawater and replacing it with just fresh... Maybe take a look at the article on specific gravity and salinity posted at www.wetwebmedia.com>
I did do a partial water change a week before everything started and I haven't been able to find a new filter for my Fluval system (small town pet shop hazard, I will end up having to order it from the internet), so I just rinsed the sponge filter out. We have well water and haven't had any problems with it, but could that have caused everything to go out of kilter?
<Yes, possibly... you might consider having your water checked for you and your aquarium use... and do what I do... get a small Reverse Osmosis unit for drinking, cooking and pet-fish use>
I did turn up the aeration system after I added the triple sulfa since it seemed to create a film on top of the water, and have left it up since then.
Jazz did die sometime last night, as I had feared he would. He was my favorite. Thanks for the link to WetWebMedia, there is a wealth of information I will take time to read through. Also, if there is a good "Salt Water Aquariums & Fish for Dummy's" or maybe a "Guide for Panicky Pet Owners" book you recommend, I would like to have some references on hand with color pictures if possible.
Again thank you for your time and advice.
Sincerely, Millie Opela
>>
Do take a look at some kanucklehead's version of the way marine aquariums are supposed to be titled "The Conscientious Marine Aquarist"... a good read, and full of nice pix.
Bob "immodest tonight" Fenner

Re: Chocolate Chip Starfish ...
I removed him last night when I saw absolutely no more activity from his little feet. Someone suggested it might have been a change in salinity, but salinity has been fairly constant between 1.022 and 1.023... I'm using an Aquarium Systems SeaTest Plastic Hydrometer for warm water aquariums. Can you recommend something better? or is this okay? water temp around 78F >>
>>
This is a fine (accurate, precise) brand, type of hydrometer. It is what I have used for many years.
Bob Fenner

Water Density Measurements...
First off I just want to say what a great book Conscientious Marine Aquarist is. It has been invaluable to me and its the first book I recommend to anyone who's asked me about getting into this hobby. I have a question about reading my hydrometer. I feel kind of silly, but none of the tables I've seen for temperature adjustments have made sense to me. I have a hydrometer which is calibrated at 78F. For my water at 82F, it gives a reading of 1.024. What is the true specific gravity/salinity of my water? And more importantly, how do I adjust the reading for those 4 degrees? Thanks a lot.
>>
Hmm, the "true" specific gravity? In all likelihood it is very near the 1.024 value that your hydrometer is calibrated to... and I wouldn't obsess about the absolute spg at any length... there are a couple of variables, artifacts if you will, that influence hydrometers readings on the basis of temperature... (compression and gas solubility issues...) but these are far less important (as is real near-seawater density questions) as doing your best to keep spg about constant... by pre-mixing your synthetic water, topping off occasionally with fresh...
Bob Fenner, who thanks you.

Trusting Hydrometer
Hello-
First off thanks for your devotion to this hobby. 
<To hobbyists and the planet>
I recently moved and had to make the change from well water to city water. Upon setting up the tank (75 g.
with sump, skimmer etc.) I had major problems. Lost all shrimp, inverts etc. the first two days. All that
is left is a green Chromis and a Sailfin tang. At first I thought the problem was lack of dissolved
oxygen from disturbing the DSB, (and maybe part of it was) but after reading your articles and FAQ's I was
concerned about my salinity, it seemed as though I was adding more salt to my water than I normally did to
get my "bobber" hydrometer to read 1.023. I went out and bought a new Hydrometer swing arm). To my horror
it registered off the chart, above 1.030.
<Yikes>
I felt/feel horrible. I exchanged a few gallons of water for fresh water, but I don't know what the s.g is at or
how much to change it a day, I know you say not more than .001/24 hr, but this is hard if I am off the scale.
<Still, better to do gradually at this point...>
I am having trouble believing my instruments, this is a bad feeling. Should I invest in "refractometric means" of measuring salinity. Sorry this is so long, please advise.
<The refractometer is a nice tool to have/use, and valuable for research, having lots invested... but a decent "regular" calibrated hydrometer (and/or one to check it against that you can trust) should yield sufficiently accurate and precise measures. Sorry to read of your losses. Bob Fenner>
Thanks,
John Gray

Refractometer
I have a Refractometer and a Hydrometer (deep six) which do you consider a better choice?
<Mmm, better choice?... Well, the refractometer is decidedly a "better choice" for accuracy and precision of measure of actual salinity... And the hydrometer is the "better choice" for ease of use (though not as accurate or precise) in measuring density/specific gravity. I would likely use the latter for most daily, occasional use.>
I used 5% NaCl solution to calibrate the refractometer and my salinity of my tank, which read 1.023 with the Hydrometer, read 1.017. I cannot convince myself which is better.
<Mmmm, you may be becoming "too involved" here (like myself, we would likely lose on Jeopardy (tm) due to too much considering, thinking about the "real" answers... when a simple, general sense of what is involved is all that is necessary). Please read here: http://www.wetwebmedia.com/spg_salinity.htm
and the FAQs beyond.
Be chatting, Bob Fenner>
Alex

Hydrometer (addition of salt to koi pond)
I need your help in testing how much salt I need to add to my pond. I have done a partial water change and I need to know how much salt I can add.
I bought a "SeaTest Hydrometer" and I need to know if is possible to test *my Koi pond water with this. If so, what should the reading be on the meter for a pond with plants. Thanks for your help.
<Mmm, not really useful/practical to use a hydrometer for salt additions to ponds... the small amounts of salts in such applications are not easily, precisely, accurately measured by such a tool. The long and short of what I sense you want to know is "just how much" salt to add... as in per the volume of your system, end results of the addition. I would guesstimate how big (gallons... as in about 7.5 gallons per cubic foot... or by filling with a watch... and figuring how many gallons per minute in filling a "pickle bucket" of determinate volume), and add (incrementally, over a period of days), about a pound per one hundred gallons. 
Much more to say/state... if you were interested in "how much" real salt you have already, and to augment you might look into a conductivity meter (rather than density measure with a hydrometer) or other "marine aquarium" salts measuring gear... Do take care in how much, how soon you add salt to your system... as the rapid die off of algae, sometimes beneficial nitrifiers, increased osmotic pressure... can be too stressful to your livestock (fishes, invertebrates and plants)... 
And more to the point (at least mine) is "what do you hope to accomplish" by salt addition?
If any of this is incomplete, not clear to you, let's keep discussing ahead of application. Bob Fenner>

Hydrometer accuracy?
Okay. I have heard that the floating hydrometer that I have (Marine Enterprises about 13" long, calibrated at 75 degrees), although supposedly a very good one, may not be accurate. I also wanted to be able to test from my tank a little easier. So, I went out and got a SeaTest Hydrometer by Aquarium Systems. It immediately jumped to 1.0295!!!! My floater always reads 1.024-1.025. And, yes, I did knock the bubbles off of the SeaTest float prior to reading the results.
Which one is correct?
<Very likely the floating unit is closer to what is real>
What should I rely on?
<Please read here: http://www.wetwebmedia.com/spg_salinity.htm>
My calcium test is not working as advertised and I am wondering if the salinity might be a problem. Carbonate hardness looks okay at 110.
Linda Swenberg
<Good lessons to be learned here re accuracy, precision, the "nature" of tests, testing. Bob Fenner>

Plastic Hydrometers
Hi there,
Currently, I'm having two brands of hydrometer. One is from aquarium systems and the other one is from marine enterprise inc. They're both giving me different set of readings. Which one should I trust ? What would be the effects be (inhabitants consist of fishes and corals) if the SG level is high (let's say it's above 1.026). Thanks.
<Plastic hydrometers are known for this. I would use the one that reads zero with RO water.  Some people average between the two.
As long as the new water matches the old water and the SG is between 1.023 and 1.028 (a bit high) you're alright.  Craig>

Plastic vs. glass hydrometer
Anthony, Again, I can't tell thank you enough for you advice.  
<truly a pleasure>
I thought I'd share with you some news today.  You mentioned in my original question that there must be a simple answer...I think you're correct.  On a whim, I took a sample of tank water to work with me (I'm a veterinarian), and checked the salinity.  My refractometer read 1.017!! I couldn't believe it.  My
hydrometer at home is telling me 1.024.  
<heehee... piece of crap plastic hydrometers... I don't know why they even make them. Don't get me wrong... the cheap glass hydrometers can be equally inaccurate... but they don't stray. They are consistent and can be trusted after a single comparison to a reference point like a refractometer for those that cannot afford one. Plastic hydrometers can be corrupted in so many ways- junk.>
I was so dumbstruck, I checked it twice more on separate refractometer.  One read 1.016 one read 1.017.
>Please tell me this is the likely cause of my problems.  
<hard to say... but very stressful indeed. And the difference in success between species was the difference in tolerances perhaps>
If this is it...I'm not sure whether to laugh or cry.  I have closed off my top off, and assume that it is best to allow natural evaporation to gradually return the salinity back to normal.
<its not that scary low that you need to add salt. I'll agree>
Jeff
<best regards, Anthony>

Refractometer 2/28/03
I recently purchased a refractometer designed for salinity measurement.  After calibration, I noticed that it was way off from what I thought I had in my tank.  Using a plastic SG meter, I measured 1.024; with the refractometer, it was 1.029.  I keep the plastic device clean and free of build-up, particularly on the pointer.  
<very good... and for all of the daily FAQ readers: it is a necessary habit to give your plastic/glass hydrometer a rinse with distilled or deionized water after every use to prevent mineral build-ups that will skew readings in time>
With another, brand new plastic meter (from another company), I also get 1.024.  I read up on refractometry, especially regarding its use in determining the SG of urine.  
<I hope there isn't a seawater v. urine analogy coming <G>>
In that context, I read that the accuracy can be affected by protein.  
<dammit... ;) >
Reasoning that even with a good skimmer there is dissolved protein in the tank water, I thought that this might account for the discrepancy.  
<ahhh...no>
After all, a display tank will have more dissolved in it than just sodium chloride.  
<the amount of proteins/incidentals in urine is... ahhh... very different from habitable seawater. (Although I have seen some aquariums in my travels that were so neglected that it looked like the fish were swimming in piss). Refractometers are used everyday in seawater by science and aquarists alike in the tens of thousands of unit numbers. The problem with your refractometer is either simply that it is a defective unit... or, more likely, that it is a hobby grade unit or a handheld unit. Handhelds are slightly effected (more so) by temperature than table tops (although the difference would not be so great to explain the .005 dif you noticed). Furthermore... those $50-100 hobby models are dubious if not junk too often. For that kind of money, you could get 2 or 3 top shelf glass hydrometers that are much more accurate and never need calibrated.>
I would be curious about your experiences with refractometry to determine SG/salinity. thanks tom
<if you do have a lab grade or table top refractometer, then I am honestly at a loss to explain the discrepancy short of defect. Refractometers are nifty toys... but really not necessary. Use your plastic hydrometer for convenience and safety (no matter how many times I call them junk <G>) and have a decent $20-50  professional glass hydrometer on hand to spot check the plastics periodically with. Best regards, Anthony>

Store owner looking to measure saltiness
I own a local pond retail store and I need a tool to accurately measure salt in my koi pond do you sell this tool?
<Mmm, no. We don't actually sell anything but the books we produce, but you can likely buy a refractometer (most accurate, precise tool... from most any wholesaler that carries marine gear or etailers. A bunch are listed here: http://www.wetwebmedia.com/marlinks.htm
Bob Fenner>

Refractometer Problems
Hi guys, just picked up one of these units...
<Phil here wishing he had a refractometer.>
the unit says it is calibrated to 0 when shipped, I used a couple of drops of bottled spring water and got a SG reading of 1.004, then with tap, same reading, then with tap I boiled for a few minutes, same reading, then tested tank water 1.027, tested tank water with old hydrometer 1.022, should I think of the refractometer as accurate (not against the hydrometer as I know the refractometer is more accurate, but wondering why the reading of SG with the plain water used), or should I adjust that 1.004 reading down to 0 and then consider my tank readings to then be accurate, I already adjusted it down to 0 and now am getting a tank water reading of about 1.024.....Thanks again...
<Hmmm... I would check with the maker of the unit.  It could be that the refractometer was damaged in transit to your home.  But if I was in your shoes I would just adjust the reading as you have done.  Hope this helps!  Phil, who is going to check his SG using the "plastic box"... LOL>

Refractometer Problems
Try testing your refractometer with RO or distilled water. "Spring" water comes from the ground and has mineral content read by the refractometer.  Same with tap and boiled water would/should actually be a bit higher still as the actual water evaporates from boiling.  Try it with pure water. 

Hydrometer
Hi guys, looking forward to the new book, it will hit Canada I hope?.....
<indeed... we have several distributors of it waiting for it in CANADA <G>>
I have a question, I use an old "deep 6" swing arm hydrometer, I always mix my salt so that it is the same SG as my tank (.024),now I know about these being calibrated at a temp of 75f,my FOWLR tank is always at 80-82f.....am I still at .024?,any idea what I am really at?, does it matter as long as consistent?.....Thanks again....
<mostly the latter (consistency). Published charts of the temp correction of salinity over a wide range reveal very little appreciable change. Not even noticeable between 75 and 80 F on a plastic hydrometer. No worries. Anthony>

Hydrometers
Hi Bob,
<Hello Tyler>
I have read your articles regarding the care of one's salinity and I agree that testing in a separate container helps prevent breakage; however, I recently bought a new glass hydrometer made by Living Sea, and it is labeled "Marine Enterprises SALTWATER HYDROMETER/THERMOMETER specific gravity 75°F".  The problem that I have is that the chart that I have for converting specific gravity to salinity was designed for an instrument calibrated to read 0 in freshwater at 60°F---I'm presuming that the instrument I now have is set to read 0 in freshwater at 75°F---how might I compensate for this dichotomy (or where might I find a conversion chart for 75°F hydrometers)?  Or does the difference in index temperatures matter at all?
<Does matter, or should I state "it can". Likely at the tank temperature you're going to be at this device will register a couple of thousands (0.002) low on actual specific gravity. You could do an actual check (with water of calibrated temperature and raising it to tank temperature) to see what the difference actually is. I would do this and make the mental adjustment (that is, that a measure of 1.025 is likely to read about 1.027). The usual note here: More important than the actual specific gravity is its constancy and even more important the composition of the media...>
Thanks for your advice,
Tyler Reynolds
<Welcome. Bob Fenner>

Re: Hydrometers
So the difference will be arithmetic, not geometric or parabolic?
Or is it simply too similar to warrant distinction within the boundaries of 1.020 and 1.025?
<The latter. The relationship is not arithmetic, but differential, however "close enough" w/in the "nuts and bolts" of actual aquarium practices to be so here. Bob Fenner>
Thanks,
Tyler

Measuring Salinity... the long way around the barn 6/23/03
I have a TDS meter and I was wondering if its reading could be used as a measure of salinity which could be converted to specific gravity.
<really not necessary/ideal>
I got a link to an interesting site in the forums, but I can't get a good correlation between what my tank reads on the TDS meter and its specific gravity. I was hoping you could enlighten me.
<use you instruments instructions or a good conversion web site to work in reverse. A good average for seawater is 32ppm (about 1.024 SG)>
My understanding is that a TDS meter basically measures the conductivity of water (so many miliSiemens/cm) and then transforms that reading to parts per million.
<yes... but it can be influenced by other solids/additives you put in the water>
Conductivity is related to the solids dissolved and should increase as salinity increases. Can such a TDS ppm reading be converted to salinity?
<you are an engineer aren't you <G>?>
If it does, what is the salinity or TDS reading that corresponds to say 1.025 specific gravity at 80 C?
<your father was an engineer>
TDS meters are fairly inexpensive nowadays.
<ahhh... a glass hydrometer (not plastic!) is more reliable, does not need calibrated... and costs about $6>
It seems they are fairly accurate and it would be nice if they could be used for more than gauging the health of the RO membrane in an RO system.
<OK... but over thought/unnecessary IMO>
Thanks for your help. Henry
<best regards, Anthony>

- Conductivity & Salinity -
Quick question: I have recently acquired a Milwaukee conductivity monitor. I want to use this to monitor the salinity of my tanks, but I cannot find a table for converting conductivity to salinity at a given temperature. I have looked all over the Internet. Any idea where I can find a table or graph? <Well... my only tool available here was the Net, so I used Google to find this: http://www.radiometer-analytical.com/all_resource_centre.asp?code=112&s=go
I think you might find the information you need there, but you should also contact Milwaukee Instruments.>
Thanks, Steve.
<Cheers, J -- >

Hypo-salinity and Hydrometer Accuracy
Hello Bob, Steven, Jason, and the rest of the crew,
This is my first question for you so I want to say that your site is wonderful and has provided me with a wealth of information, which has allowed me to be much more successful at this hobby than I could have ever thought.  Without this site, I would likely be one of those in and out reefers who drops the hobby after a year, now I'm hooked for life.  I'll keep this short, no story behind why I'm asking.  I am having a problem with hypo-salinity treatment.  I believe that my hydrometer readings are off.  I have three: a Deep Six, a Sea Test box-style, and a floating glass (with a built in thermometer and made for aquarium, rather than lab use).  All three read differently!  So I chose to trust the floater because I have read the others can drift over time and
both are not brand new.  I have conversion charts galore, but they are worthless if you don't know the calibration temp of the hydrometer or if the hydrometer is not accurate anymore.  I believe I am failing to maintain a proper 1.009-1.010 SG and that my true SG is more like 1.012-1.013 (this would be true if the floater were calibrated at 60F).  After three weeks in hypo and several FWD's my fish are still showing spots and scratching a bit.
>>Do know that there are documented subspecies of Cryptocaryon irritans that do quite well in low salinity environments.
>Questions:  Is there any way that I can mix a test sample of water with a controlled amount of salt (I have Instant Ocean brand) at a specific temperature in order to test the accuracy of each hydrometer?  
>>Yes.  I would first calibrate with distilled water.
>Is there any other way for me to be sure that I am at the proper SG level?  
>>Yes!  Invest in a good quality refractometer!
>Even if I am now at 1.013, is it possible for the ich to be so virulent as to survive that, and continue to re-infect my fish?  
>>Yes.  This would necessitate the utilization of copper or formalin treatments.
>Can the spots I see be bacterial infection from the parasites bursting out during FWD's?
>>Yes, but not so likely as to keep the same appearance of the ich (at least not in my own experience, secondary bacterial infections really LOOK like infections).
>With sincere gratitude, Manny
>>Do a search on Terry Bartelme, he's written quite a bit on ich, treatments, prevention, etc.  Then, I would search the reefs.org library, as well as Advanced Aquarist for the same.  I've only recently learned of the ich subspecies, both instances mentioned by folks working in Hawai'i.  Hope this helps!  Marina

- Specific Gravity & Temperature -
Hi, Hope all is doing well there.  I have a 75 gallon F/O tank.  My fish are:  2 percula clowns, 2 lemon butterflies and 1 coral beauty angel. Please tell me what you recommend for tank temperature and specific gravity.  I have been keeping the tank at 76 degrees and the specific gravity at 1.021.  Thank you, James
<James, I'd shoot for 1.025 for salinity - it's what the ocean is typically at. As for temperature, you could go a little higher, but there's nothing wrong with 76F - 76-78F is ideal.
Cheers, J -- >

Specific Gravity Specifics!
Hi Scott
<Hi there!>
My salt water aquarium has been running now for a week now since setup. I mentioned to you that I am trying to sort my heat issues out and in the last week my tank has been running close to 80 deg Fahrenheit.
<Not too bad...>
What I need to know is does the temperature affect the salinity reading?
<It can>
I hope this is not the case as I have my salinity measuring 1.022 which is perfect right?
<Ya' know what? I used to be a believer in lower specific gravities for a lot of reasons, but after much experimenting, I've concluded that natural ocean specific gravity (generally 1.024-1.026) is the way to go...I shoot for 1.025>
I should have the fans in soon and also gonna be doing one or two mod.s to the hood of my tank so I can get more air to circulate.
<Excellent! That can make a difference in the heat buildup...>
Thanks Again Regards, Ziad Limbada
<My pleasure! Stay cool! Scott F>

How Do I Use This Thing?  Float Hydrometer Primer
>Hi, I'm setting up a 110g saltwater tank.
>>Cool.
>I was given a glass Saltwater Hydrometer (by Marine Enterprises), approx 12 inches in height. The problem is: I have no idea how to use it. No instructions were given with it.
>>No problem.  They don't come with instructions for the most part.  It's a float hydrometer, and it's really easy to use.
>Is there a website with step by step instructions on how to use the meter properly. This meter has what looks like little pellet balls and some type of wax in the bottom of it.  
Thanks for your response, America
>>Easy-peasy, America, no website needed.  What you will need is something to put some of the water you wish to measure the salinity of into that is TALL enough to let the hydrometer float freely.  My favorite is a device I make myself out of clear plastic tubing (you can get this at the fish shop) that is capped and sealed on one end (needs to be watertight).  About 1" in diameter is fine.  Then, you fill it with the water, drop in the hydrometer, and you want to look at the lines on the really skinny part.  There will be one fat one that's pure water, a salinity or specific gravity of 1.000 - that's pure water.  (Btw, don't measure especially cold or warm water, make sure it's room or tank temperature - between 73F-82F - as this WILL affect the proper measurement).  So, the hydrometer should float so that the lines BELOW this 1.000 mark are what hit the top of the water - this measurement is your specific gravity.
It is at this point that I MUST urge you to start buying books, because (and please don't take this as an insult, we all start from a position of no knowledge), if you don't know how to use the simplest hydrometer made, then I fear there is much other invaluable information you don't have as well.  There are MANY excellent beginner books, Bob Fenner's "The Conscientious Marine Aquarist" is one, and you may wish to search for books by Martin Moe, Jr., C.W. Emmens.. aw heck, to http://www.reefs.org/library/reading/  and http://www.reefs.org/library/reading/beginner/beginner.html and search the database for books on saltwater for beginners.  Also, you will find (if you have regular internet access) that the talk forums for our site and reefs.org are EXCELLENT for quick information.  Our sister site is http://www.wetwebfotos.com/talk - know that many of the folks who answer questions here are "on duty" there.  If you do join, let 'em know that Seamaiden/Sea Maiden sent ya.  ;)  All my best, and Happy Holidays.  Marina

Hydrometer trouble - 12/18/03
Hi crew, I've been visiting and reading the FAQ everyday for a year now and you have helped me many times. <great to hear> Thanks for all your hard work it is truly appreciated. <tanks a million, bud>  A couple of quick questions, yesterday I decided to do some maintenance on my sump/fuge which is a 30 gal that feeds my 55 gal reef.  My SG has always been 1.024 using a floating glass hydrometer. <very well> I replaced most of the sumps 30 gal with premixed saltwater, problem is after completing the water change I broke my glass hydrometer. <DOH!> I went to the LFS and bought the plastic "box" version, did a read, 1.030 (as you always say YIKES!). <Don't trust it> I want to start replacing 2 gallons per day with freshwater to get SG back to 1.025 area. <Woah!!! Get a second or third opinion. Try either another glass hydrometer or if you know someone with a refractometer>  I understand that consistency is more important than accuracy, however should I trust the "box" or get a new glass hydrometer for calibration purposes? <New glass and another opinion>  I don't want to over react based on a possible faulty reading from the "box". <agreed!!> Also if the 1.030 is accurate, based on 85 gal total water volume, minus 100# LR, do you think 2 gallons per day a reasonable starting point for moving SG .001 per day? <That should be about right you could do a little more>  I've read of similar events in the FAQ's, just looking for a "mental" calibration. <get a second or third opinion if possible> As always thank you for your kind response. <My pleasure. ~Paul>
Mike

Hydrometer Recommendation
Hi All,
<howdy>
I am looking for a recommendation for a Hydrometer / Refractometer for measuring specific gravity.  
<your best bet/value IMO... a glass hydrometer (do spend the extra and get one of the $20-30 units). These are arguably more reliable then even the handheld refractometers>
I have the usual cheap one, but am told I should get a better one for hypo salinity treatments in QT tanks, etc.  If
you have a link of one or can comment on the refractometers on marine depot (around $70), I would greatly appreciate it.
Thanks, Andy
<the cheap hobby grade handheld refractometers are good... but not as great as one sometimes here's about. Reliability in refractometers is to be found in table mount models (not influenced easily by temp) and on lab grade equipment. Refractometers that are made cheaply overseas (imported $15-25 and retailing $50-80) are not always as good as you might hope for them to be. Whichever you choose... simply avoid using the plastic hydrometers as a primary. Anthony>

Hydrometer Recommendation 2/3/04
Thanks, do you have a link where I can find an acceptable glass one (perhaps a brand name)?  I checked marine depot and a couple other places online and can only find the cheap hobby ones.  
<no easy link here I can think of. I have used the high end hobby ones like Marine Enterprises brand with satisfaction FWIW. Anthony>

Refractometers 2/14/04
Quick question regarding refractometer.  Love this site!  
<thanks kindly>
I have a plastic hydrometer, which from reading on this site is not the best of readers, nor was I aware of the cleaning.  
<correct... they are not that reliable or durable. A quality glass hydrometer is actually the best all around. Do keep both and compare the glass as needed>
Which I am doing now....  I work in a lab, we have a refractometer which is checked daily with two controls.  One is DI water, reading should be 1.000 +/- 0.2, the other is 8% NaCl with a reading of 1.032 +/- 0.3.  The controls are at room temp.  I see calibration is mentioned, and I note on the refractometer that is calibrated every 6 months.  Now can I use this for my salinity checks?  
<certainly>
I brought a sample in before and it was quite a bit lower than my reading with the plastic one.
<not surprising... some of those plastic hydrometers are easily corrupted (dried minerals from poor cleaning, dropping/jarring... and QC>
This refractometer is a Reichert TS meter. If I bring in a sample from home, the temp on that sample is quite lower than my tank ... my tank is at 78. Will this make a difference in reading?  
<the diff is small but please do simply heat the sample up. Use a water bath to float your sample in (its container/baggie) to warm up>
This is a lab refractometer (I work Hemo and Chemistry) we use this refractometer for urines, though usually this is only used after a problem with our automated instrument.  So can I use this, does the temp make a difference.  
<yes... but there are published scales for compensation... mere fractions of a difference though>
When I do any testing on my aged salt mix (to replace weekly changes) I always have the temp matching the tank.
<very important...yes>
Thanks so much Kris
<best regards, Anthony>