Upside down cat fish

Question
I have a 28 gallong tank with 9 fish in it. The temp is 76 degree, I change a 1/2 to 1/3 water every 2-3 weeks, They eat 1-2 alge bisquits and flaked food once a day.  I have the biowheel filter on the tank.

I recently took 2 pleco out of the tank because they were too big and were attacking each other and making everyone in the tank uncomfortable.  All of the other fish would hide in the plastic plants.

Since I have taken out the plecos everyone inthe tank seem much happier swimming around and more out in the open.  THe upside down catfish however has turned grey to very light grey and is sitting on the bottom of the tank.  He doesn't swim around like he used to... It has been almost 3 weeks that he just sits there.  He will get up and eat but then goes back to the same place and just sits there.

I have a 10 gallon tank I can separate him if he is sick

What should I do

Answer
Billie,
Do you have any place inside the tank that the cat can hide in? They are nocturnal fish and like to hide during the day. If they can't they will stress out and go pale. If other fish are picking on him, then I would remove him from the tank and place him in his own until he is feeling better.