What Is Wrong With My Fish?

[Dmbandstef]

My fish have been twitching their heads, rubbing on rocks, and one of my cories ( the only cory showing signs of illness) keeps swimming to the top for air. I have been treating with mardels quICK cure. It treats multiple illnesses but I do not know whats wrong. Please help!

 

[fluttermoth]

How often are you seeing them rubbing on things? And how often is the cory going up for air, as that is actually a natural behaviour for them (they get some of their oxygen from a small bubble of air they keep in their gut).

Oh; have you tested the water at all? How big is the tank and is it cycled? Exactly what fish do you have?

 

[Dmbandstef]

in my 55 gallon there is 1 blue acara, 1 rainbow shark, 8 black skirt tetras, and 4 green corys. I have only seen 1 cory go up for air and he also rubs on the gravel. My blue acara spends most if his time in his cave, but i see him twitch and rub everytime he is out. The shark only rubs on the gravel but i have not seen him twitch his head. The tetras dont show really any signs of illness. I got the water tested about a week ago and the only problem was low pH but i bought a bottle of ph neutralizer. I think the ph might have something to do with it but not sure.
oh and the tank is cycled.