I have a 20 gallon set up with all of the proper equipment and maintenence with a figure eight puffer fish and a reticulated hillstream loach (they ignore each other, zero problems ever). I keep a tank of pond snails to feed him on a regular basis, along with mysis shrimp and krill. He's normally a very healthy eater and quite energetic. But since yesterday he's ignored a snail in his tank, shrimp, and bloodworms. He was at least acting normally until just a little while ago when he started acting very lethargic and his stomach began to look dark. Please help!