Sick Guppy?

[FurFinFeathers]

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.

 

[BerryAttack]

haven't cycled the tank?
any schooling fish should be in a long tank and never a high because they swim distances and not up and down.. the aggression from them if not put the in proper numbers can affect your other fish.
corydora should always be in groups of a min of 3, but i like seeing them in 6+.. always looks nicer and they school better.
do a large water change on your tank with treated water and you should see an improvement if it is just the ammonia etc are high.. but you'll need to keep doing water changes until he continues. that'll all i can say without a pic to look future and not knowing your water stats.

 

[FurFinFeathers]

No, the tank is cycled, the sponge filter is there temporarily, until the good bacteria grows on it and I can transfer it to a different tank and make cycling that one easier. The tank my guppy is in is completely cycled, with the ammonia at zero, nitrates at zero and nitrites at zero. He's been with the other fish a good long while, and they've never had any problem with him.