I had 2 Mystery Snails and 2 Ghost Shrimp in a 3.5 gallon cycled, heated, filtered, live planted tank and recently upgraded to a 20 gallon heated, filtered, planted 20 gallon tank. I was running both my new and old filter from the 3.5 gallon in the new tank. I transfered the substrate, plants and decorations from the old tank to the new one. I noticed that my Mystery Snails were looking ill after a couple of days and weren't eating. They were hanging out of their shells, sliming and looking near death. My API test kit showed 0ppm Ammonia and Nitrite. I did a water change of 20% anyway, with conditioner treated water. They actually looked worse after the water change. I have had them back in the 3.5 gallon for 2 days with the old filter with one cartridge in it (I put the other one inside my canister filter in the 20 gallon to continue to help the good bacteria colonize). They have either been closed up or hanging out of their shells the entire time. Not eating. I have also been giving them an air bath once a day. One of them came out of his shell yesterday during the air bath and scooted around a tiny bit. He looked withered and terrible, though. Is there anything else I can possibly do for them right now? I've even been playing them this "animal healing music" from Youtube- lol. I just wanted to give them a nicer house and this has turned into a nightmare!