Agnelfish lying on bottom.

My angelfish has been lying on his side at the bottom of the tank for about a week now. Occasionally with a lot of effort he can get upright and swim but it seems to take all his energy and can only do it for a few seconds. What should I do?

Some additional info:
About a month ago he had some large white bumps on his side. I don't remember exactly what I diagnosed it as (lymphocystis maybe, and not ick for sure) but it wasn't supposed to be life threatening and would clear up. So I did some additional water changes and a week or so later it was cleared up. He seemed a little more lethargic but seemed better. a week or so after that he was on the bottom but upright. the next day he was on his side. I moved him to QT and he has been the same since.

Water parameters are 0-0-0

 

Wow...to both the fish's problem and your parameters. You should have at least some nitrate reading 5-15 or the likes. As far as the fish goes...you didn't treat him with any meds? Just did water changes? Hopefully someone with angel knowledge will come along.

 

It's possible that it has an infection and is trying to ward it off. Are the gills really red? Has it been eating?

 

If you used meds they might have affected the nitrate, which could be why it is at zero. I don't really have many ideas. Could this just be an older fish?

 

The tank is pretty heavily planted so the nitrate level is pretty close to undetectable.

I wouldn't say his gills are really red. maybe a little more than normal. Since he isn't swimming he doesn't really feed normally. I have given him sinking pellets and they seem do be disappearing but I don't know if he is eating it or the filter is getting them.