gulping at the surface

[Slipperypete]

please and thank you

 

[thebiggerthebetter]

That's not true at all. As long as there is surface agitation that serves the same purpose as an air stone. Op, have you tested the water?

Agreed.

OP, at this point with so little useful info I can offer three causes:

1. Ammonia/nitrite (ok does not cut it, please let us know the test results in ppm with a reliable liquid test kit)

2. Not enough oxygen (either too little stirring in the tank and/or too high a temp; it's easy to measure temp)

3. Illness, bacterial or parasitic, like gill flukes or in fact could be others.

1. and 2. are easy to eliminate.