Specific Gravity

jswinberlin

Reefing newb
What is the right specific gravity for a FOWLR tank? Is it true you should add .002 when using a needle refractometer? For example, if the water is 78 degrees and the refractometer reads .021 it is really .023?

What is an acceptable fluctuation in specific gravity?

Thanks for any input!
 
Natural seawater around most reefs in the world is 1.0265 or 35 ppt. There is no reason it should be kept at anything other than that.
An ATC (automatic temp compensation) refractometer calibrated with a calibration fluid will read the salinity as it is.

Ron Shimek's Website...Critters
"Coral reefs are generally located in areas that have salinities in the range of 35 ppt to 38 ppt. Most of our corals, and the associated fauna including fishes, will live best at those conditions (Weber and White 1976). Most organisms, even osmoconformers, can survive for brief periods in salinities well outside their normal range. But if maintained for longer period outside of that range they will be stressed and eventually will become so damaged that they will die even if returned to their normal salinity. Higher salinity is slightly more tolerable to these animals than is lower salinity, and adult animals are more able to withstand the extremes than are the juveniles or larvae."

"The bottom line for salinities is simple. There is simply no reason at all to maintain the salinities of our systems below normal reef conditions. All reef inhabitants will suffer damage from prolonged exposure to lowered salinities. Invertebrates kept at low salinities often die within a few days to a few months. Given that corals, sea anemones, sponges and some other invertebrates have no old age or senescence (or to put it another way, they are immortal), low salinities result in a quick death. Some mollusks, crustaceans, and most fish kept at low salinities die of kidney failure; it just takes them longer. A fish which dies in a couple of years in a hyposaline aquarium may have had the potential to live more than 20 years had the salinity been appropriate."
 
Wow, that's higher than I thought. Mine is at around 1.023. Maybe this is why I have never been able to keep turbo snails. I'm going to try to raise it gradually over the next few water changes until it reaches the right salinity. I'll add only the desired salinity until it reaches it so that it doesn't shock the fish. Does this sound like the right method?

Thanks for the help!
 
Okay, conflicting info here folks. It has been recommended to me that my FLOWR tank will be fine, and should be kept between 1.019 and 1.025 and that my current 1.023 is perfectly acceptable. In reading this thread, it sounds like the tolerances are tighter and higher than I have been told from various sources. My sources are from several books, several stores and several forums.

So what's it going to be? Should I aim for 1.025 on the low side and a max of 1.026 on the high side?
 
You can choose to listen to whoever you want. The link I posted above is the recommendation from Ron Shimek, PhD in Marine Biology.

Here is another by Randy Holmes-Farley, PhD in Chemistry. (Who is Randy and what is the Reef Chemistry Forum? - Reef Central Online Community)
Reef Aquarium Water Parameters by Randy Holmes-Farley - Reefkeeping.com
"For reference, natural ocean water has a salinity of about 35 ppt, corresponding to a specific gravity of about 1.0264 and a conductivity of 53 mS/cm."
"Ron Shimek has discussed salinity on natural reefs in a previous article. His recommendation, and mine as well, is to maintain salinity at a natural level. If the organisms in the aquarium are from brackish environments with lower salinity, or from the Red Sea with higher salinity, selecting something other than 35 ppt may make good sense. Otherwise, I suggest targeting a salinity of 35 ppt (specific gravity = 1.0264; conductivity = 53 mS/cm)."
 
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