Saltwater aquarium salinity problem/question?

Question

I can't seem to get the salinity specific gravity up to 1.024. i add more salt and it goes up for a bit but then settles back down to 1.021 to 1.020. I feel like i've already added quite a bit more than the 1/2 cup per gallon as recommended on the instant ocean package that i used. I have a 37 gallon viaaqua tank. a fluval 204 canister filter. 12 pounds of live rock, 40 pounds of live sand and 30 pounds of regular sand (aragonite). 5 scarlet hermits and 5 nassarius snails. i'me using a red sea hydrometer (swing arm). my other water parameters seem to be okay. ph about 8.2. temp about 82 F. nitrates and nitrites okay.

i've been taking out 2 gallons of water - adding more salt to the bucket, stir it up and then pour it back into the tank when it looks to be dissolved completely. no air stone. and its usually the next day when i notice the SG has gone back down again. I don't understand it because i was expecting the salinity to go up as the water evaporates...

i understand the effect of sawter temperature on specific gravity and have made the necessary adjustments. my concern is that the S.G. is not calculating the salinity properly. I know my water is on the hard side. maybe 240 to 300 ppm - according to test srtips. could this be affecting the S.G.?

Answer 1

Don't pay attention to the "1/2 cup per gallon" given in the directions on the salt. In my experience, this is hardly ever an accurate measurement to get the salinity high enough for a tank with inverts. If anything it usually works out closer to 3/4 cup or more for me. Go by the readings of the hydrometer, just make sure that there aren't any air bubbles attached to the needle if you use a floating needle variety, and rinse the hydrometer well between and before each use to make sure there isn't dried salt making the float "stick" or weighing it down. The glass floating hydrometers are more accurate, but can be harder to read if there's any current (they are also much easier to break!). Take an average of three readings from different points in the tank and take an average if the readings seem to fluctuate.

The temperature would only affect the salinity by about 0.001 for every 10oF change in temp, and the salinity should go down as the water evaporates. Hardness shouldn't be a factor. If you have "salt creep" along the filter or rim, this could cause the salinity to go down.

Answer 2

check for what temperature the hydrometer is calibrated to give a reading at. Higher or lower water temperatures may cause it to read differently. Another thing is are you adding the salt directly in the tank? you should always premix the salt befor you put it in the tank. If you are getting a low reading and keep adding salt wait till the next day to take a sg reading. As the salt disolves in the water the sg will rise. 1.020-1.021 is ok you are still in the safe zone for most marine inhabitants. So dont worry to much for now let the salt disolve and take another reading tomorrow and if it is still low then remove 5 gallons into a bucket and add about 1 cup of insant ocean salt, mix it up really good and let it sit for an hour. I sometime like to take an airpump and an airstone and put it in the bucket where i am mixing salt to let the water airate. then add it back in wait an hour or so and take another sg reading.

Addition: Hmm thats interesting water hardness may affect it but if you keep adding salt the sg is going up. Try getting a different hydrometer see if the readings are the same. seems more like a faulty hydrometer. i mean its simple science you add salt the salinity will rise. You are right as the water evaporates the sg should and does go up. Befor you add anymore salt to the water go get a different hydrometer and see if the readings match. Like is said befor 1.020-1.021 is still in the safe zone for pretty much any marine fish or invert. It wont have any terrible outcome on the inhabitants of the tank so leave it be till you get a new hydrometer.

Answer 3

you seem to know alot about your aquarium. anyways back to the point, im thinking its the brand of salt your using. try looking for a more reccomended salt brand.try asking your local pet store or ask anoter question on yahoo answers. hope this helps!