Hi all,
only thing i can think of is toxins in the water supply as i have moved so suply is different, only thing is im unfamilliar with toxins and which would cause the breathing issues
Ryan if your water company have being doing water main work in your area they will have put a large dose of chloramine in your water supply. Even if you use a de-chlorinator, like Prime or Amquel, that de-toxicifies chloramine this will effect your biological filtration as the conversion of ammonia to nitrite and nitrate uses a lot of oxygen. We had a lot od cases of this in the winter after the big freeze.
What you have done, and what Doodles and DMAC have suggested is the best bet, unless you can get another water source and change the water with that. I use rain water, but I appreciate that not every-one has access to a relatively clean rain-water supply, could you get RO from some-one?
The other possibility would be to pre-treat the water with plants as thay will preferentially take up NH3 and stop it entering the filter.
The reason your plecs are effected is that they are from water that is clean and quick flowing naturally, this means that they have evolved in water supplies with lots of dissolved O2, and don't have tolerance to lower O2. The more rheophilic a Plec is, the more Oxygen it will need. If you have a highly rheophilic fish from cold water like a Salmon (or some of the
Chaetosoma spp.), it will have a very high O2 requirement
If you had a Gibby or Common Plec in the tank they would be less effected as they come from water that can be oxygen depleted, and they can gulp air and extract the O2 from it like a
Corydoras can.
cheers Darrel