Is it necessary to add calcium when keeping shrimp, snails, and/or crabs? My current test kit doesn't have a calcium test to it, but my next test kit that I get will definitly have it. Also when I first researched the margaritia snails I have I didn't see anything about water temp. Now I see that these snails are actually a cooler water snail. My water temp is between 78 and 80 consistently. Does this mean they're going to keel over soon?