Silly question.

I'm raising the temp of my tank while I'm cycling to make bacteria grow faster. When I lower the temp for the bimac, does the salinity of the tank go up or down as the water gets colder?

Salinity would remain constant, as long as you don't add or remove water with a different amount of dissolved salt. If you put a kg of salt into a tank and it all dissolves, increasing or decreasing the temperature isn't going to make the salt come out of solution nor make more dissolve. You've added a kg and no more or less can dissolve than that.

Generally, temperature has little to do with the amount of dissolved ions in a solution, though granted temperature change is used to supersaturate a solution, but thats well beyond the scope of aquariums. Hope that helped and didn't confuse.

Cheers!

Ah, I thought that specific gravity would change with temperature.

I believe that specific gravity does change with temp - based on my home distilling I know it affects the reading, so I think what happens is the reading will need to be adjusted for, just not the amount of salt in the tank lol. - could lead to problems :grin:
For my homebrew the sg comes with a table with a variety of temperatures.

When I redid my tank, which had been full of feeder crabs, the salinity was off the scale. Don't know how this happened as I only add fresh as evaporation occurs. Crabs seemed to be fine in it though.

It does change slightly with temperature differentials, but only over a huge scale, not the small increments (+/- 3 degrees) that we work with...you should have nothing to worry about.

greg

The refractometer I have adjusts automatically to suit the temperature of the water to give an accurate reading.
Very usefull because I often make up my saltwater mixes in my garage which is cold and the water temperature is often about 50 - 55deg F whereas my tank is about 78... obviously I heat the water up before adding to tank but water temp does make a difference to a hydrometer's readings

That is my concern. My tank is 83F right now and I'm going to lower it to 68-70F before my octo takes it as a home, so my reading will change greatly. However, I know that salinity is a little low right now. 1.023, and I want it to be 1.026 when I add him. Will it rise with lower temperature, or would it go down?