Would it be a bad idea to move it to a tank off the system where I have some other plecos thriving?

Ph is 7.5
Ammonia 0
Nitrite 0
Nitrate is around 20 ppm
Temperature is 75f
And now that I look at them they do look a little emaciated? What are they supposed be eating? I try to offer a varied diet yet I've honestly never seen them eat, and I originally got them back at Catcon.

I keep losing my Chubby plecos for no obvious reason, they're juveniles (4") and in a 40breeder on my central system. The tank is bare bottom with a couple pieces of aged driftwood and some PVC. The only tank mate is a single Kobia guianensis. I've been feeding them like all my other plecos ...

I saw no blood at all. Not entirely sure what it could've been but it was the first thing to come out.

Was relatively solid and didn't fall apart but was squishy and took up just about the entire abdominal cavity, and the fluid was yellowish but clear and seemed to have the consistency of normal fish mucus.

Well i lost this guy the other night, opened him up to gather some insight and the and what came out was a big yellowish blob, there also seemed to be a bit of fluid in the abdomen.

I've a bunch of coconut caves and stacked rocks. I haven't noticed much aggression towards them but the Altolamps and the cylindricus seem to be a bit territorial with their caves.
Forgot to mention that this catfish seems to be deficating normally.

He's in a 40 breeder with 3 juvenile Ophthalmotilapia ventralis "Kipili Village", young group of Pundamilia spec. "Red flank", a young Altolamprologus calvus "Chaitika", an Altolamprologus compressiceps "Dwarf Sumbu", 2 Neolamprologus cylindricus, and three other cyclurus.
I keep the temperature at ...

Could anybody help id this disease that's affecting my Lobiobagrus cyclurus?
He's been like this for weeks and just keeps getting worse, I had a similar issue with a yellow bullhead that went on for months before she finally passed. I really don't want to loose this guy or my other three.