Hello, A few days after a water change ago I noticed my one Guppy just sitting at the bottom of the tank. I noticed him doing the same thing the next day and today I saw him doing the same thing then he was standing strait up on his tail trying to swim. The guppy does not visually have anything wrong with him. The guppy is now swimming at the water surface. I am quite concerned. I have melafix and primafix on hand. What should I do? Thanks.