crabs & snails dieing what to do

Is it worse if its too low or too high? I know my lfs has their sg at 1.019 too reduce stress.

They aren't running at hyposalinity but they are running low enough to show why drip acclimation will help avoid osmotic shock. If you have a tank at 1.023 the stock isn't going to fare well coming from a 1.019. Raising salinity is something you need to do slower than lowering it by the way.
 
I never do anything with inverts but drop them in and haven't had a single one die on me yet...and I've had my fair share!

When you say, 'no, no copper', does that mean you bought the test kit and checked, or you're just assuming there is none in there?
 
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