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Help, I recently got a group of Pleco fish, Bristlenose and the longfin variants from someone, they are nearing 5 years old but some are younger and we’re spawned in this tank when the other person had them.
One of my big males has floated up to the top of the tank and I thought he was dead, he has a bloated stomach and his mouth is wide open but when I scooped him up he wriggled. If I let him out of the net he swims down but floats right back up.
After reading some other forums I attempted to feed him deshelled peas but he’s not interested at all.
None of my other pleco are acting the same and are as healthy.
He’s trying to swim occasionally but is mostly floating from one side of the tank to he other.

Tank temp rn is unknown as I just found that my heater is not working. Could this have made this happen? Why have the others not been affected?

Sounds like diet issues or constipation to me but who knows. I had a Bristlenose randomly die on me during a water change a half year ago or so(looked abit like you described it except he didn't float to the top), it also had a bloated stomach, a bit weird since I barely fed any protein heavy food into the tank but guess he must have hogged the occasional bloodworms or something.

It could also be something like kidney failure if the water quality was very bad for a long time. In that case there is really nothing to do about it. I rarely see floating catfish get better.

You could try epsom salts, but I doubt it will help.

Good luck,
Eric