I am new to the site and really am a novice when it come to aquariums. One of my fish I think is dying and I do not know what to do!! Her eis what is happening I believe he is a tetra he is blue (not that that matters) but there are 4 of them all together and a red tail shark and a sucker fish. All the other ones are FINE they have lived together for probably 2 years but this poor guy is still breathing his fins look fine, ther eis no rotting or white specks on him he looks normal, but he is lying one the bottom of the tank. When you swoosh the water around he does get up and swim but he swims on his side or upside down, then goes back the the tank floor. What should I do?