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FAQs about Specific Gravity, Salinity Maintenance

Related Articles: Specific Gravity, Salinity, Product Review Marineland Labs/Aquarium Systems Hydrometer, Part 1 By Steven Pro, Choosing Synthetic/Natural Seawater, Major/Minor Seawater Constituents, Frequent Partial Water Changes

Related FAQs:  Spg 1, Spg 2, , & FAQs on Spg, Salinity: Importance, Science, Measure, Anomalies, & Treating Tapwater For Marine Aquarium Use, Seawater, Seawater 2, Seawater 3, Seawater 4, Seawater 5, Seawater 6, Reverse Osmosis Filtration, Test GearUsing Hyposalinity to Treat Parasitic Disease,

Steps to Nirvana: Pre-measuring, mixing and storing make-up water... adding a bit of "just water" (perhaps bolstered with supplementation of sorts) on a daily basis... Most of the world's oceans... 1.025... the Red Sea and a few other places a bit higher...

Raising Salinity 1/7/11
Good Morning!
<Hello Joan>
Yesterday morning at about 4:45AM my sump sprang a leak!
<Not good.>
The ATO poured about 4-5 gallons of RO/DI into the tank and lowered the salinity from 1.025 to 1.022 in about an hour (by the time I realized this was not evaporation). It took all day to fix the leak (it was a seal on the bottom of the tank somewhere). Got a powerhead running and an airstone going but it just took a long time to try and seal the leak. Just hope it holds until Monday when we get a new Aqueon Proflex #4. We added back 4-5 gallons of new saltwater. It wasn't until around 9PM that we added the additional salt water because it wasn't ready. The salinity still reads 1.023. What would be the best way to raise the salinity back up to 1.025?
<To mix new saltwater at a higher salinity (1.040) and slowly add over a two or three day period.>
How badly did the sudden drop in salinity hurt my critters? I would imagine all of my other readings are equally lowered. My PH dropped from 8.15 to 7.99 yesterday (after ATO added all that water) and then after adding the new saltwater came up to 8.04 this morning so I would imagine that my alkalinity is down as well (easily remedied just add Seachem Reef Buffer). My display tank is 110 gallon and the sump is about 30 gal. if that helps.
Thanks for taking the time to help!
<You're welcome. James (Salty Dog)>
<In the future, please delete your personal information below your name unless you want thousands of people to view this.>

Re: Sailfin Tang Compatibility, now sys. temp., spg.  -- 12/01/09
two last questions - what is a good temp for the water in the tank - mine now is at 82-84. I cant seem to get it adjusted to 82, its either 86 or way to cold at 76.
<Optimum for reef inhabitants is 76-82 -- I tend to hover around 78-79 on my tanks.>
And while your answer about my problems with the Sailfin tang - what do you suggest for a good salt level? I've kept mine between 19 and 21 seems like the fish like that - well I guess except for the Tang :(
<Do you mean 1.019 and 1.021? This is too low -- aim for 1.026.>
Once again, thank you for all the helpful information - we can read and read and try and try - but its always nice to have someone answer the weird questions.
<Absolutely, we're glad to help!>
Hope you have a WONDERFUL holiday season.
<Same for you and yours, Cecilia.>
Cecilia Lester

Raising Salinity 5/18/09
Hey there Crew, hopefully there is someone there who can help me with what is probably just a simple math question.
<I hope so too.>
I've been running my tank at hyposalinity to deal with an ich issue. I'm now ready to raise it back up.  Total water volume is 220 gallons. Salinity right now is 1.009. End goal is 1.025, raised up over the course of 2 weeks. I can mix up about 20 gallons of water at a time.
<14 days sounds reasonable for this change. That would be a change of one one-thousandth per day, this or slower should work for you.>
So say I want to mix up a 20 gallon batch of water that I would normally put 10 cups of salt mix in. However, because I really want it to up the salinity
at least one thousandth when it gets mixed into a 220 gallon system, I'm thinking I might put like 20 cups in instead of 10.
<I don't know of a magic formula to accomplish this for you, especially when I don't know the actual water volume of the tank. I assume when you
say 220 gallons, that that is the tank size and not the actual water volume.>
Anyway, is there a formula I can use to determine how salty that would make the main tank?
<Perhaps someone else will chime in Grant, but what I would suggest is small water changes with natural sea water salinity each day to gradually raise it up, I would not recommend hyper salinity makeup water to boost the tank salinity.>
<Josh Solomon>

Re: Sick clownfish? Spg change   12/23/07 Hi Bob, Thanks again for the advice. I am taking it and leaving the fish alone for now. I have set up a hospital tank, just in case, that I hopefully won't have to use! For future reference, what do you think is the right time frame for adjusting my water as I did? <No more than a thousandth of spg per day... and if this much change... no more than a thousandth every two-three days. BobF> Thanks, Jason

Salinity and water changes  10/25/07 Hello, I would like to start by saying that your site and staff members have been essential in helping me maintain a healthy saltwater aquarium for many years. <fabulous> I recently upgraded to a 125 gallon tank which I plan to maintain as FOWLR. I have about 150 lbs of LR and a 6 in. live DSB, SG will be kept around 1.022. <This is too low. Although most fish can tolerate lower salinities, the micro-crustaceans and other inverts which put the "live" in live DSB and live rock need a salinity much closer to natural sea water (ideally, 1.024-1.026). Please see here: http://www.wetwebmedia.com/spg_salinity.htm> The tank has been drilled and drains into two connected sumps (30 & 20 gallons respectively). The 30 gallon houses a refugium with a live DSB, LR, and two types of macro algae. The 20 gallon has been divided into two chambers, one with my remora protein skimmer and the other holds a Rio 1300 return pump. My livestock consists of 1 juvenile Koran Angel, 1 Powder Brown Tang, 1 Tiger Wardii Goby, and about 40 Nassarius snails. Since this will be my first adventure with a tank this size, I was seeking your advice concerning husbandry. Given the inhabitants and system, how much water should I change on a weekly basis? <5 to 10% weekly or 20 to 40% monthly. Please see here: http://www.wetwebmedia.com/water.htm> Also, do you recommend keeping the SG relatively low if I do not plan to add corals? <No, please see above.> Thank you for your time and advice. Kiet <De nada, Sara M.>

Deep Sand Bed, Low Salinity System 9/21/07 Hi. Greetings from Alaska. <Hello from Chicago.> I have a 55gal. FOWLR with quite a bit of fish. Bicolor angel, Raccoon B/F, Fox Lo, Royal Gramma, Flame Hawkfish, Tomato clown and a Yellowtail damsel. <I would call that very heavily stocked, even overstocked.> I am a big fan of hyposalinity system and that is not as a treatment but as a method of my hobby. <I have to disagree with you here, keeping fish in anything other that natural as possible conditions is exceedingly stressful over time and leads to an early demise.> I am running this tank for more than a year now and I have no disease or any problem on my fish during this period. <Unfortunately I don't think this will last over the long haul as the conditions take their toll.> I am planning to buy a HOB refugium and make a deep sand bed in it. My question is: Can a anaerobic nitrifying bacteria form or thrive in a deep sand bed with a salinity of 1.010 SG? Thanks for your response. Larry <The bacteria will colonize this area, there are many species that live in all different salinity levels. However I encourage you to reconsider your approach.> <Chris>

Re: Techniques for raising Salinity- adding salt to the sump -- 09/19/07 Suppose I just use a high concentration of salt water as Make Up water in the auto-top off. Tanks uses about three gallons a day. That seems to be even better than water changes. <Yes, this is good plan. -Sara M.>

Water Change Mistake, Specific Gravity Level 10/7/05 Hi guys, <Hello Mark.> Thanks for all you do through the WWM site. It's been invaluable to me as I work with my tank.  <Glad to her we have helped.>  I have a 58 gal Oceanic Reef Ready with about an 8 gallon wet/dry. Tonight I was doing my weekly 10% water change and inadvertently refilled with RO/DI fresh water from the LFS. Imagine my chagrin when I realized it! <Uh-oh.> My sg is now 1.021. I think it was around 1.023 before the change. I haven't run a panel on the water to check Ph, Alk, yet. The water had been buffered, so at least there was that. The question: Will my two clown fish, 20 hermits, 20 turbo snails, or live rock be adversely affected by the rapid drop in sg? <As you already know this SG is a bit low. Having said that while it is not an optimal level if you slowly bring it back to normal through extra water changes over the next few days I would not expect to see any long term damage. Should you see any die off I would expect it to be your invertebrate life not the fish.> Kicking myself for not "taste testing", <A refractometer is your friend.> Mark <Adam J.> 

Salinity  09/13/2005 Hi Crew,   I live in Jamaica where our temperatures average in the 90's. I have a 200 gallon marine tank FOWLR, the water temperature is in the high 80's and I was wondering what salinity I should keep my water at?  <Temperature and salinity are really non related as far as any significant change that would occur.  But, to answer your question, anywhere between 1.021 to 1.025.  James (Salty Dog)> <<Mmm, but the hydrometers most folks use are calibrated for lower temperatures... I would keep the apparent density near 1.021, 1.022. RMF>>

Dilution Equations    3/2/06 Hello <Hi Fargo. John here this afternoon.> Spent several hours on the web and your website.  Couldn't find much to help, but I was wondering if you guys might have an equation that would help estimate how much fresh water needs to be added to lower the specific gravity of an aquarium by a certain amount.  I have tried the standard equation of m1v1=m2v2 but have not been able to make it work. <Conservation of momentum? uh?> Then after I lower it, need to figure out how to increase very slowly as to not stress the fish.  Trying not to take a shot in the dark and do it as controlled as possible. <regardless of what you do, I wouldn't increase or decrease the specific gravity by more than around 0.002 at any one time. For determining the quantity of freshwater, it really is easy my friend - just need to calculate a ratio: Resultant specific gravity = (Vol1.SG1 + Vol2.SG2)/T Here, Vol1 is the amount of water remaining in the tank, and Vol2 is the amount of water you are changing T = tank capacity (Vol1 + Vol2 = T). SG1 = specific gravity of water in the tank SG2 = specific gravity of change water.> Cheers and Thanks <Welcome! John.> Fargo

Raising Salinity??? Hello again Mr. Fenner, I recently emailed you about copepods & offered to buy you "little brown bottles" @ the SuperZoo-What a great show that was. <Agreed> I got tired of asking everybody @ the show if their name was Bob Fenner. Maybe your next book should have a picture so all of us can put a face to the name. <Hmm, not that attractive. Should have sent you to: http://wetwebmedia.com/BobFBio.htm > Anyway, my 50g tank has been w/out habitants for 2.5 week now w/ the temp @ 81 & salinity @ 12. My quarantine tank is aprox. the same. My question is: when do I start raising the salinity & to what level is optimum.  <In another two weeks... a thousandth per day... to 1.025> The two fish in the q/tank are a 3" red sea Sailfin tang & a 2" flame angel. I am considering adding gobies, hawks, Firefish, cleaner shrimp & getting the 50g tank ready for reef.  <It likely goes w/o stating that you will be waiting a few weeks plus after returning the existing stock...> I will be adding a 180g 3 sided room dividing tank after the hot Las Vegas summer is over. I have seen flames & sf tangs in reef tanks before & wonder if they will eat soft corals or sponges if I add them to the 50. Is it worth a try? <Yes, worth trying... the Flame may nibble... more so in a 50 than a 180... but likely no big deal> And will it do any harm if they do eat them? <No> Thanx again for such a great website & sharing you expertise w/all of us! Also, (last question) What is your opinion of the "eco-system" set-up & their "garlic" product for ich? <The Eco System looks like a nice product (no first-hand experience), but very pricey... Garlic, have heard folks say it does some good in some cases... am not convinced it is a panacea. Bob Fenner> Craig

Re: Raising Salinity??? Mr. Fenner, You look a lot younger than the mental picture I had of you.  <Ha! Images can indeed be deceiving... I always thought women had a staple in their belly-buttons from perusing girlie mag.s as a youth! Carved in stone back then> I read your bio & now I value your opinions even more, quite impressive resume and it sounds like you really do enjoy life to the fullest.  <Hmm, guess this is where I should chirp in, "Don't believe everything you read" or such...> Especially the Sushi part. If you are ever in Las Vegas, I know a few great sushi spots & would be happy to treat you. <I've heard there are some good ones out your way> Now my questions. A week from today my main tank will be 4 weeks w/out habitants and ready to start raising salinity, then adding my quarantined fish (Red Sea Sailfin & flame angel). My tank has grown algae to the length of an inch or so on the rear glass, along w/the copepods mentioned before.  <Great> When I put the 2 fish back in the main tank, will they proceed to eat the algae & copepods? <Some of both yes> Should I clean some of it off? Or should I leave it be & not feed the fish for awhile.  <The latter> Will they overstuff themselves & throw all of my (perfect) water levels off? <Very likely not> Also, If I add a orange spot goby or similar bottom dweller to my quarantine tank for 2 wks. min), will I have to add some sand to the small tank? <A good idea> Thanx again in advance! Craig <You're welcome my friend. Be chatting. Bob Fenner>

Re: New tank setting it up Well, Bob I put in dechlorinated tap water in my 55 gal. tank and let it stand for a day or two. I mixed in a 50 gal. bag of Instant Ocean into the tank with 2 powerheads and a Millennium 3000 filter running. After 24 hrs, I put some of the water in my SeaTest hydrometer and the needle went all the way up to 1.030!!?? Is this normal? Should I add more fresh water? <Normal, yes... there really isn't 50 gallons of water in your 55... not just due to displacement... do the math... Length times width times height in inches divided by about 231 cubic inches per gallon... So yes, remove a proportion of the current volume and replace with just freshwater> I also have a CPR Bak Pak2 skimmer which I have not installed yet, should I put it in already? <Please read: http://www.wetwebmedia.com/marineSetUp.htm> Thanks for taking the time to answer my questions Bob. I know that you are a busy man and you do not have to do this so thanks again. <No worries, be chatting. Bob Fenner>

Salinity for Reef Tanks In Alf Jacob Nilsen books he said to keep salinity at 34 parts per thousand .Some protein skimmer makers say keep it at 31 parts per thousand what is the best salinity for reef tanks. And if it is to high how should it be done lowered  -R. Gibson. <Most reef keepers are aiming for a specific gravity of 1.023-1.025, which corresponds to about 31-34 ppt. If you wish to lower, slowly add extra freshwater. Change no more than 1 ppt per day for extra caution. -Steven Pro>

High specific gravity Good morning, My problem is that in my 80 gal. reef, the specific gravity has gotten up to 1.026. My feelings tell me that this is a little too high.  <not really unnatural for many reef animals, but indeed high for aquarium husbandry. Things run smoother a lower down on SG in aquaria> I've been adding RO top-off water but that hasn't seemed to have any effect.  <that sounds unusual... and I hope the RO water isn't raw (you need to aerate it and buffer it for 12 hrs before such use)> Should I change out maybe 10 gal. of water and just add that RO water back into the tank without any salt in it to try and lower the specific grav. I'm kind of at a my wit's end . <its really not that big of a deal and doesn't stray fast either. Keep a closer eye on it in the future to prevent it. In the meantime. Test your math for the water change first on a smaller scale (10 gall of 80 gall with fresh) by mixing 7 cups of tank water with one cup of fresh water and then test the SG. If so... fine but go slow. Good and bad things should happen slow in a well planned tank. Kindly, Anthony><<Mmm, have to take out some of the solute-laden water and replace with less solute-laden... to reduce Spg. RMF>>

Mixing Salt - 2/13/03 Hi guys, Have a quick question about mixing salt. It's been a year since I had my take up and going, but now I'm close to starting again.  I had been using Coral Life salt, but have switched to Tropic Marine Salt.  Question is this....The Coral Life always had a little sheet that described approx. how much salt to add to so many gallons at a set temp.   <Temp has no measurable effect within safe tropical temperatures on your hobby hydrometer... no worries here at 76-80F> The box of Tropic Marin has nothing.   <Excellent salt! The best IMO> So....Is there a set guideline to how much salt I should be adding to my water to get a SG at 1.023 to 1.025. and at what temp. Thanks Bryan <Easy my friend... they are all very similar. Its about 1/2 cup sea salt per gallon of water. Anthony>

Specific Gravity - 2/17/03 Hey Guys- Got a question about maintaining specific gravity...I premix my RO water and heat it and circulate it and use it to top off and do my regular water changes...but what formula do I use to take into account for the increase in salinity due to evaporation? Thanks <Evaporation and water changes are two different things, of course. There is no formula. You need to add fresh water daily to your marine tank to maintain the normal and original salinity on set-up. Your weekly/monthly water changes are then simply adjusted to match that salinity. I'd advise using a glass hydrometer to compliment your plastic one (unreliable). Anthony>

- Semi-Auto Top off - Jason, <Good evening...> I've reviewed as much info as I could find on your site regarding auto top offs and my primary concern is the failure of a valve or switch. <I think perhaps I wasn't entirely clear - I was trying to convince you into a different 'way' to change the water; not in small, constant amounts, but in one fell-swoop - more akin to using buckets, but also incorporating your desire to use these tanks. I do not propose you go full-blown auto top-off, but rather crank the valves by hand.> How reliable are the Kent float valves. <They work.> What's the most reliable switch? I like the simplicity of a float valve but it would be difficult to build in redundancy as one could by using multiple switches. <Again... these items add unnecessary complication - consider just putting a hand valve where you might use a float switch.> Regards, George <Cheers, J -- >

Reef specific gravity 1. What should the salinity be for my reef tank. I have a 55 gallon with 75 lbs of Fiji rock and live sand. I have a few soft and hard corals, a few anemones and many different invertebrates. <I keep my reef tank's specific gravity as close to 1.025 as possible. Make sure the water temperature is correct for your hydrometer as temperature affects the reading. You can find this answer and many others by reading the articles here http://www.wetwebmedia.com/marine/index.htm and beyond. Hope this helps Don>

Saltwater too Salty - 8/28/03 Dear WWM Crewperson: I just made 32 gallons of saltwater for my storage batch, and I made it a bit strong, around 1.030.  I would rather not dump some out and add fresh water.  Can I add some of my top-off water to my water change bucket at the time of a 2-4 gallon change in order to bring it down to 1.025?  Thanks, Rich <Yes you can. Should be no problem. Bob Fenner>

Too Salty (12/28/2003) Hello everyone I have a 90 reef running for 4 years now and for some reason my salinity is running high 1.028 how do I go about lowering that to 1.026 without affecting my ph, alk.? I just ordered a refractometer should be here Monday otherwise have been using the old plastic style, I know Egads those dreaded plastic testers. I have been reading through the sight and have not seen a ? regarding high salinity and how to lower safely. I do water changes aerated with RODI water as I also do with top off water that is buffered to 8.3 for ph, like wise when I add my salt I have been backing off on salinity mixture but this has not lowered the salinity of the tank water and have been doing this for some time. if you need more info I'll be glad to let you know, your help is grateful Brian <Those plastic swing-arm hydrometers are notoriously inaccurate. I love my refractometer--great investment. Before changing anything, I'd suggest you use this to measure the SG of your tank and your replacement water. Of course you're topping off (replacing evaporated water) with buffered RODI water with no added salt, right? If you kept the salinity of your replacement water at 1.023 - 1.024 and do small water changes 1-2 times per week, your tank salinity should drop gradually. I like to keep my tank at 1.024. Others prefer a bit lower or higher. Hope this helps. Do keep us posted. Steve Allen>

Back To Normal (Returning Fish To Normal Specific Gravity) Hi all, <Hey there! Scott F. with you today!> I was wondering if I needed to slowly raise the salinity ~5ppt a day from 14ppt back to 35ppt to return fish back to my main system after a month in hyposaline conditions. Or, can I safely do a drip acclimation that spans that range in salinity? It seems that water changes with NSW conditions would be safer but the drip would be easier, please advise. Thanks, Ryan   <I'd be more comfortable with the gradual increase to 35ppt. The drip method can work, but it might be a better idea to do it the slow way...HTH! Regards, Scott F.>

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