This morning I woke up and went to feed my 20 gal high tropical aquarium when I noticed my male fancy guppy, who had been completely fine yesterday, wad laying at the bottom of the tank. I see nothing visibly new with him. He seems completely, one hundred percent healthy except for the fact that it seems he can't swim very well at all. He will swim up to eat, but then go back down to the bottom of the tank. He's only got a couple small tears in his tail but they're nothing new. The only new things I have added to the tank recently is a sponge filter that I'm cycling for my betta tank, a platy and a corydora catfish (both of which are very healthy). His other tankmates are five danios, one other cory and an otto sucker fish. Ammonia, nitrate and nitrate levels have not changed. Any diagnosis for my fishie, or better yet, treatment? Thanks.