This morning while doing my cosmetic checks I noticed in one of my tanks my fineline plecostomus (sailfin x) floated to the top, upside down and stiff. When I went to net him out he started moving his fins very weakly. I have currently separated him into a net breeder box in the tank.
I'm hoping for opinions on the cause and how to fix this issue.
He has no obvious injuries or imperfections.
Running an AquaOne Nautilus 1400canister filter
Temp 71 F (we had a heater failure overnight (temp was at 68F when failure noticed) and have replaced it- current cold tank may be the issue? we usually keep it at 75-77F).
Population: 2x 2in Tiger Oscars, 2 x 2in Chocolate Cichlid, 1 x 4in Ghost Knife, 2 x clown loach (3 in, 5 in), 2 x 2 in fineline pleco ( one is the sick one).
Tank cycled for 2 months prior to adding fish, then added no more than 4 fish per month. Finelines were added 3 weeks ago.
Tank has ornaments and driftwood, no live plants.
We have a 180G that we will be moving them all to in a few months when our house build is finished.
Parameters: I have used the API Master Freshwater test kit
Nitrate: 10 ppm
ps. Today is water change day.
Any help with this little guy would be appreciated