My son has an ADF frog in a 5 gallon hex. I've been noticing some leftover food lately, so I moved one of my msytery snails from my 20 gallon to the 5 gallon hex. The next morning I noticed it floating with some slime hanging off of it. I removed it to the 20 and it took about a week to recover. I checked the water in the hex tank and all was well. So, I was puzzled and waited about another week, did a 50% water change and tried adding a different snail last night with the same results. The odd thing about it is that when I remove them, they float, but will open up and act like they're trying to move around but simply can't stop floating. They'll even let me turn them over (while under water) without retracting into their shells. I checked the water again this morning and the tank is cycled with less than 10 nitrates, so I just don't understand it. Can anyone think of why the snails are reacting this way? I used to have a snail in this tank with no problem before, so I don't believe it's an oxygen issue. It's as if something in the water is irritating them but I can't figure out what it could be. (there is a terra cotta pot, and two java ferns...and the adf is doing great.) I like the idea of one of the snails in there to help with leftover food since it's hard to get into that tank easily to remove uneaten food daily. I really dislike this hex tank design for that reason alone.