Ok finally got a few pictures.
The ones from behind him show the bulge.
The ones from the side look worse than they are - the white is odd but not as odd as it looks in the pictures.
The thing the pictures don't show well is on the very left where the lateral line goes up there are some red spots ...

Also - we were planning on seeding the 65 gallon with the filters from the old tank - but the bb is probably very low now because of the antibiotics... We would love to move him but are scared to stress him when he's not 100%. Though if it's a "condition" and not an illness then better to have him ...

Thank you for responding! We are going to try to post a picture.
He has a few round marks on his lateral line that look like scrapes?
You can tell he's trying to poop! But it's not happening. :(
Will post more details with the picture!
Oh wood chips are Sera Catfish Chips.
We are afraid to move ...

Hardly pooping or eating for a month!
Water since meds - .25 amonia - once was .5 before a water change
Temp 80-82
PH 8-8.2
GH?
KH?
He's about 13" in a 25 gallon - we've been waiting to put him in a 65 until he's better!
He's 10+ years old. No other fish.
Aquclear 50 & Tetra 40 - they need rinsing ...

Thank you very much for responding! He does seem a tad bloated - though eating his zuccini.
Is one slice of zuccini (round slice on a veggie clip about 1/4 to 1/2 inch thick) a day enough for a fish that big?? What about algae wafers? Should we try add one a day? Should we fast him for a day? Or ...

We have a common plec about 13". He usually decorates the tank like crazy!
All water parameters are normal. Our water is hard and alkaline. Always has been.
Temp is in the 80 degree range.
Water change of 30-40% once a week.
2 hanging filters.
Tank about 30 gallons.
Always has been.
Used to share ...