maria wrote,
It seems that every corycat I get eventually succumbs to the same
disease. The only symptom is that the fish loses its balance and cannot
swim or lie on the gravel straight. Eventully the fish dies...

I can put out a few ideas; water may lack electrolytes - add a teaspoon
of salt per 5 gals... may be a lack of humic acids - add a piece of
driftwood or a little peat moss in your filter... How often do you
gravel vac (?) rotting fish waste and uneaten foods within the gravel
causes hydrogen sulfide... Are you sure your catfish are getting enough
to eat (?) a lot of people think they eat the waste from the other fish
- they are good, but not that good - they need food... High levels of
DOCs (dissolved organic compounds) = little or no dissolved oxygen near
bottom due to organics consuming the oxygen - high nitrAtes... Flavo
bacteria - internal bacteria treated with a medicated food twice a day
for 10 days and an a broad spectrum antibiotic in the water such as
oxy-tetracycline. Unlikely a bacterial infection without the other fish
getting it also. I would suspect something to do with the water
parameters............ Frank