I have a 55 gallon aquarium , I have 7 platies (had 8), 4 black skirt tetras ( had 5), 1 gourami , 1 plecos, 2 snails, 3 shrimp. I'm very worried because I lost 1platie and 1 tetra over night, 1 more platie is very lethargic was hidding in the dark but I put her in the same tank in a nurserie...