I have a 26 gallon tank with 2 platys and 4 zebra danios. I've had it for about 3 months. I had another platy and 2 balloon mollies that died this week from a fungus (I think) . Anyway, I have added salt to the aquarium once and then did not add it again when I've changed the water. I didn't add it cuz there were so many differing opinions on adding it, but now I found out that the lfs I buy the fish from puts it in all their tanks. Now, I'm thinking of adding it again, but I dont' know how much of the salt I orignially put in is still in the water. Is there any way to tell? I don't want to add too much salt and kill the fish.