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FAQs about Specific Gravity, Salinity Importance

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: Science, Measure, Maintenance, 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,

MANY biochemical, biophysical phenomena are influenced by water density, osmotic pressure, the percentage salts make up of seawater. You want to shoot for dynamic equilibrium.

Salinity Stability in a Reef Tank ~ 12/30/08 Hi There, <<Hello>> I am wondering the importance of absolute salinity stability. My conductivity can vary from 50 to 53 (using Neptune controller) due to various factors from inputting more Kalkwasser than is evaporating, skimmer overproduction, water changes, etc. I am working towards stabilizing this # but I am wondering if I should worry and care to try to stabilize this? <<A good question'¦ Depending on a coral's origin many do experience such fluctuations in the wild, seemingly without harm. I've heard tell of Xeniids growing on freshwater waste pipes. And corals living in lagoons often experience wide fluctuations in salinity due to the tides and the effects of evaporation and rainfall. But as far as captive care goes and the induced stresses re, it is likely best to keep such fluctuations to a minimum in the aquarium. To put your specific situation in better perspective and to maybe make it more understandable to a wider audience, the Conductivity readings of 50 to 53 (mS/cm) equate to readings of about 33 to35 ppt for Salinity and 1,024 to 1.026 for Specific Gravity (depending on exact water temperature and which conversion chart/calculator you use). Though I prefer to see reef tanks stabilized more towards the upper end of this scale, I think these readings/fluctuations are acceptable>> Speaking of skimmer overproduction, when I do a water change for several hours after my skimmer produces a lot of wet skim (almost water) <<Many systems experience just the opposite (a loss of skimmate production)'¦ You may be stirring up detritus and releasing colloidal compounds that increase the foam production>> and my ORP drops by 75-100. <<This would also seem to support my theory>> As always thanks for all of the info. <<Quite welcome>> Best, Bryan <<Regards, EricR>>

Increased salinity danger?  11/16/07 Hello Crew, <Msieu Miles... From the Latin (like Miles Standish) in ref. to soldiering> I hope you all have a great Thanksgiving and happy holidays. Also, thank you for increasing our understanding and ability to keep a part of nature that many of us would never be able to experience any other way. <A pleasure to share> Now I only have one quick question. I try to keep my salinity at about 1.025 using a swing arm hydrometer (a refractometer is on my wish list, and I should have one shortly). With a second hydrometer for verification my reading is closer to 1.029. I will be taking a sample to my LFS this evening for testing. My question is how damaging is this higher salinity if proven accurate? <Mmm, marginally if within a thousandth or so> My livestock are: 1 Foxface, 1 coral beauty, 2 true percula, 1 snowflake moray, 1 settled Green BTA, several hermit crabs (blue, red, and scarlet legged), various Nassarius snails, 2 Queen Conch, 2 Trochus snails, 7 Astrea snails, small Candy Cane coral, small Frogspawn, 2 small Green Star Polyp frags, and Pulsing Xenia. The reason I've listed my livestock is in case there are varying sensitivities to the raised salinity. <Well put... best to try to maintain at any given point> Thank you to whoever responds to my query, and thanks again to all of you who help us in our endeavors, Billy Miles <Welcome my friend. Bob Fenner>

Mystery To Me.....Not to me! Drop in Salinity = Problems -- 07/30/07 Crew, <Hi Ed, Mich here.> Thanks again for all the great advice contained on your site. <Glad you like!> I am writing about my 125g reef. Details as follows: 125g; 2 sumps, each approx. 20 g Tunze filtration, skimming and nitrate reactors calcium reactor (HRC) turnover provided by Tunze stream and a larger in-line pump pushing penductors ammonia: 0 nitrate: 0 nitrate: 30 <A bit high.> temp 79-81 salinity: 1.025 pH: 8.1 (night); 8.25 (day) animals: sailfin tang; 4 small damsels; sixline wrasse; pink spotted goby; flame hawk; bluehead wrasse; assorted softies (bubble, Sinularia; open brains, many zoas, some GSP, yellow polyps) a couple of starfish and a coral banded shrimp Recently, the salinity dropped to 1.014 due to a plumbing issue. <Yikes! http://www.wetwebmedia.com/spg_salinity.htm > I brought it back up to 1.025 over a 3-day period. My issue is the corals all have deteriorated significantly and the largest star is out in the open (rare) and relatively slow moving (comparatively speaking). I also have a black cuke that has gone from huge and swift to skinny and lethargic (but not deceased). <Echinoderms are quite sensitive to changes in salinity as are many corals. This significant drop in salinity changed the shift in osmotic pressure in these invertebrates, essentially dehydrating them, which just as in humans, can be deadly.> Could the salinity drop have created such a disaster...Sinularia drooping, 'shrooms smaller, bubble receded, brains shriveled... <Oh yes indeed!> all fish are active as if nothing has happened. <Fish are much more tolerant to changes in salinity.> The tank is 3+ ears old <Hee! Does it hear well?> and has a sand bed of combined cc and oolitic sand, about 2-4" in depth.....there is about 150# of LR involved in the total system. I dose a bit of Lugol's monthly and magnesium quarterly. <And hopefully test these levels as well.> I use Red Sea salt, mixed in RO/DI water, augmented with Osmo-prep marine. Recently a Pinktail trigger died while I was on vacation, but there was no nitrate spike so I assume the sand critters (stars, crabs, etc. just had a feast). <Yikes!> Any suggestions or verification that my failure to maintain proper salinity might have caused this mess would be appreciated as would a prognosis. <Yes the salinity drop it likely the cause of your problems here. As for prognosis... only time will tell. Grunfeld from Michigan Reefers (Ed) <Poconofishy from NJ Reefers, NCPARS and Mountain-Valley Reefers (Mich)>

When should I stop? Quick Question. At what point will lowering the specific gravity adversely affect my biological filter media?  At what point will it stop to grow good bacteria on the media.  Specific #'s would be great. <NSW, near sea water conditions are best. That is, a specific gravity of 1.025 is ideal... and keeping this about here (topping off regularly, adjusting new water carefully) is very beneficial. For treatment with hyposalinity, any drop/change in spg will adversely affect nitrification. ANY. You should monitor aspects (ammonia, nitrite) daily, be ready with new water for dilution, perhaps chemical filtrants, pre-made biological filter material... if lowering spg, or raising it.>          If you want some details leading up to this question read on, if not thanks for your help!         I have a 120 gallon main tank a 20 gallon quarantine and a ten gallon hospital.  All tanks are biologically alive with all parameters in check.     The reason I have all the tanks going is that I just got a majestic angel about a week ago, I know what you are thinking but I did my research and realize what I'm up against and took 7 months of going to my LFS to find the perfect specimen.  The problem occurred when I introduced some Caulerpa to the main tank for a treat for my powder blue after a quick rinse without quarantine," bad move". I've been doing this for 5 years now, will I ever learn.  Within about 5 days the tang had some spots, I caught him gave him a dip then returned him home. Three days later you know what.  Unfortunately I'm in it for the long haul now at least 45 days.              So now I have three tanks set up and running. A ten gal hospital bare bones with a powder blue in it which I'm am treating with hypo salinity and formalin dips plus my own tank/filter creation which has a high enough turn over rate to successfully filter out that pesky littlie protozoa but allows me to segregate the bio filter. A 20 gallon quarantine tank with 8lbs of live rock, live sand, tang haven algae two power heads and a whisper 30-60 which I modified and put  bio wheels in to boost it's efficiency, one Chromis and a majestic angel.  Did I mention I have now found a few spots on the angel?   <Now you have> So let's break it down I have three tanks with ick and five fish I have to find a place for to let the main tank go fallow for about two months.  Yes. I do have cleaner shrimp but about all they're good for is making babies and stealing food from the Anemone, Its a good thing my two percula's are great protectors.  I have a written protocol for all new fish but slipped on the algae.  I always use my quarantine first then if the new fish have parasites I put them in my hospital which I will establish 1 week or more ahead of getting a new fish by a sponge filter from my main tank  then I can let the quarantine go fallow for a month while I treat the new fish in the hospital tank without drugging up the water then after one month they go back in the quarantine tank for another two weeks. I always try to keep from using meds, except in dips, if I can at all avoid it.  If there still alive after all this then they make it into aquarium paradise, if not then at least I didn't contaminate my main display. I have about a 85% success rate.  I thought I had a fool proof system. I guess the fool didn't fallow the system.                    Without the books of Bob F. and articles on this site I wouldn't have ever stayed in this hobby.  You guy's are the Bomb! <Be chatting, Bob Fenner>

Problems after salinity increase 3/6/05 I recently raised my salt level (it was pretty low). In the last two days I noticed one of my emerald crabs dead, my xenia has shrunk and my brittle star has lost an arm and had some white spots on him. Should I wait, do a water change or other? Thanks, John  <Salinity changes are very hard on inverts, and what you are describing is probably due to this change. I would suggest increases of no more than 0.003 (1.017-1.020 for example) in any one day and giving the animals a couple of days to acclimate. If you have been more aggressive than this, I would just give everything a few days to acclimate (trying to drop the salinity back down will just add to the stress). Also, I would strongly suggest checking your salinity measuring device against another aquarists, a local fish store or a refractometer. "Swing arm" style devices are notoriously inaccurate. Best Regards. AdamC.>

Gills Swollen on Green Chromis I notice the other day that my Green Chromis seems to have swollen gills. The gills seem red and irritated, however the fish still eats but not as active. I check my salinity and it was 1.028(to high) so now I slowly lowering it to 1.024. Would this cause the Green Chromis have the above symptoms? Would it be wise to place him into the hospital tank for a while? I want to get more fish and place them into the hospital tank but I am not to sure if I am dealing with a parasite or a disease. My other fish have not been effected by this. Thanks <swollen gills are not a conspicuous symptom of a given disease and may have been aggravated by the high salinity, although a true 1.028 should have been tolerable for a short period if elevated slowly (as I suspect it occurred from neglected evap top off). Observe for up to three days more... the condition stabilizes or improves... ride it out without medications (only if necessary). Else... QT for sure. Anthony Calfo>

Salinity Rob, Still a bit confused, one final question/thing about salinity. My reading indicates that when threatened with disease, ich, etc. it is SOP to lower rather than raise salinity level and increase temp ????? <Yes, in general. But it is also standard operating procedure to maintain most all organisms at/near normal conditions to reduce stress. Bob Fenner>

Lowest salinity safe for crab and shrimp? Hello again. I apologize for so many questions, there is so much to learn. I have read over all the FAQ's regarding lowering specific gravity for reduction of ich. I am leaving my tank for 2 months without fish hosts to greatly reduce parasites. <After two months, there will be no more parasites. They will all perish in one month.> There is a Lysmata cleaner shrimp and a white spotted hermit crab in there with live rock, my question is what is the absolute lowest I can reduce salinity to without killing my crustaceans? <No need to do the low salinity with no fishes, but anyhow, I would not go below 1.018.> Right now I have it at 1.019 with a temperature 84. <I would leave as is.> Regarding my 2 quarantine tanks one with a maroon clown and neon goby and one with purple tang and neon goby what is the lowest salinity possible these fish will tolerate? <I have read of treatments as low as 1.010.> If my maroon clown shows no signs of parasites and seems very healthy can I please take out the CopperSafe, it has only been in for 7 days, but she has been visibly parasite free for 6 days. <I would run the suggested course of treatment.> I know she is sensitive to copper and I want to take it out as soon as is safe to do so and put in a piece of live rock to hopefully help with reestablishing bacteria after the copper. <There are other treatment options in you do not like copper; daily water changes and freshwater dips are my two favorites.> Also is it okay to take copper out of purple tang's tank after 2 weeks even if she still has faded spots/scars on her body. <Same advise as above> Thanks again for all the wonderful help and advice, I would be so lost without your website. No one at any of my LFS can ever agree or seem sufficiently knowledgeable to trust. ~Kylee Peterson <That is a shame. -Steven Pro>

Coral health in high salinity Hello Anthony, Pete from Western Australia again. <cheers, mate... its very good to hear from you! My apologies for the delay in response, I was out of town giving a presentation to the Los Angeles aquarium society. A great club and time was had> A query regarding the adaptability of corals to water with higher than usual salt levels.  <hmmm... interesting> Shark Bay is an area with limited flushing, high evaporation and low rainfall, and as such salt levels in some places are up to nearly twice normal seawater!  <Yikes!> At our location the SG is around 1.029 rather than the usual 1.026.  <no worries here> There are some nice corals around us here, probably at salinities of 1.030 or more. Can most corals usually cope with such salt levels, or would the specimens in these areas have developed a tolerance over many generations? <some tolerance... but also some concern here for the long term viability of trying to run that in a captive system. In the ocean, at least many/most other parameters are more in line... crashing waves, high dissolved oxygen, unlimited food and dilution of waste products, temperature stability etc. The reality in your closed system will be different despite your best efforts. Higher DOC levels, lower dissolved oxygen, less temp stability, etc. To add a salinity on the highest end of the threshold to that may be too much for many coral species. I'm worried that it will be a problem. Do ameliorate/dilute the display if possible (unless this is an open system?)> With regards to our 600,000L display tank, we are pretty much stuck with the 1.029 SG because of the size of the tank and the limited available freshwater. If this salinity is a concern, the obvious solution is to collect corals (we have permission for this) from areas with similar salinity.  <yes... perhaps best at least to begin with I'm sure> However, having dived these areas frequently and seen consistently high concentrations of zooplankton, I suspect that many of the corals from this region are heterotrophic. The difficulty in feeding corals in a tank as large as ours has me leaning towards aposymbiotic species, especially as the water may be clouded during feeding of heterotrophs, which is not a good thing for a public display... it would be too hard to explain to most people - they just want to see pretty fish in clear water.  <hmmm... do you have the terms confused my friend? Aposymbiotic creatures require frequent and heavy feedings (as in "not symbiotic" and must feed). Heterotrophic means the same thing. Hermatypic corals are the photosynthetic reef builders that I think you seek. Arghh... the science of it all <smile>!> Perhaps we could identify and collect species which are known to be mostly aposymbiotic from these areas, or perhaps we could feed more heterotrophic species after closing and let the foam fractionator clear the water overnight... <I would avoid most or all heavy feeders for the big displays. Better for small displays that you can feed heavily and afford to do larger and more frequent water changes on> The alternative is to collect from deeper, "cleaner" waters just outside of the bay. Visibility here is often over twenty meters (mmm...20m+ vis...:)  <just beautiful! I hope to see it one day> so I suppose corals would be mostly aposymbiotic. We could use an underwater light meter to match the light conditions between the point of collection and the position in the tank (wouldn't it be nice if this information was given with all collected corals...).  <yes!!! very wise... please do this for all, my friend> However, this area has SG around 1.026. How would these corals take the transfer to SG 1.029?  <on the point of a .003 change... no trouble at all, I suspect> What duration of acclimation would be appropriate? <short would be fine in fact. Hours no doubt> As always, I value your input and thank you for your time. <it is my great pleasure to share my opinions and experience. I wish you the very best and look forward to hearing from you again. Pictures too when you can!> Regards... Pete McKenzie <kindly, Anthony>

Raising salinity Just Live Rock I only have live rock in my tank at the moment and my spg is 1.020. If I want to bring it up, should I still do it slowly or can I boost it in one shot since there is no livestock, per se, in the tank yet? <Actually... there's a bunch of salinity-sensitive life that is the "live" part of your rock at risk from such quick changes. Do elevate the spg at most about 0.0005 a day... by removing some existing water, adding some of higher density in its place. Bob Fenner>

Salinity & Temperature Dear Bob: <Connie> I was at a meeting of SeaBAY last night (in SF area) and learned that the salinity in my LRFO tank should be at .025, also that the temperature for my tropical fish should be 80 degrees.  Do you agree?, <Mmm, most systems will do best at near seawater conditions. About 1.025 for specific gravity... and 80 F. is about right for many tropicals... but there are arguments for keeping most cooler, some warmer. You can read about these on WetWebMedia.com> My salinity is now about .022 - over what period of time should I raise it to .025, if this is correct?? <No more than 0.001 per day.> Thank you Bob. <Welcome. Bob Fenner> Connie C.

Spg Hey crew!  I have been reading quite a bit on here lately and have come to the point where I would like a little bit more in-depth explanation of some of the topics available. <Okay> 1) I have read the Specific Gravity and Salinity articles several times ( http://www.wetwebmedia.com/spg_salinity.htm).  It points out pretty reassuringly that floating hydrometers are perfectly acceptable for the average hobbyist and that specific gravity stability is more important than a specific number. (a 1.020-1.025sg range is considered fine). <Yes... precision is often more important than absolute accuracy here>   However, when going through the FAQ's I noticed one in which Bob stated that we shouldn't really shoot for anything other than 1.025sg (give or take .001). <Also a "truism"... especially for the majority of in- or non-vertebrates kept by aquarists>   I am just wondering how close I need to worry about this.  I currently have my tanks at 1.025, but want to know if there is any importance between the two differing ideas. <Mmm, some. If really concerned I would opt for a more accurate "checker" like a better grade glass hydrometer, or a refractometer...> 2)  I also read about the dangers of acclimating a saltwater fish too quickly to a higher specific gravity.  While challenging their systems to maintain a " salt and solute" balance, are there any long term effects known other than this immediate stress? <Some longer term ionic imbalance problems and their consequent manifestations. Bob Fenner> Sincerely, Ryan A.

Thank God for your service (salinity rise) 1/20/03 I was wondering..... I had a spike in my salinity, for about a week, I was away and did not perform proper maintenance.  My salinity spiked to 1.027 in my reef and fish tank.  I was keeping it around 1.02 - 1.022 <I suspect that the drop back to 1.020-1.022 was more harmful than the "spike".  While you were away, the SG slowly rose due to evaporation.  When you lowered it, I suspect you did so fairly quickly.  Also, Natural Sea water is 1.025, and lower SG is more stressful on  corals than higher SG.  I always recommend 1.025 for a reef tank.> It seems that my Wes. Brain coral lost about a dime amount of tissue. Do you think it will grow back, hoping that is does not get a infection?  Thanks!<Probably not an infection, just a reaction to the stress of the salinity changes.  The tissue may take a very long time to recover or may be permanent, but the coral should be fine.  Also, just for accuracy sake, All corals known as Wellsophyllia and Trachyphyllia are all now considered Trachyphyllia.  HTH.  Adam>

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