Loss of appetite and lethargy w/o any external signs are probably either a bacterial infection (what I've had to deal with for 3 clowns in the past month) or an internal parasite. Here's what I did to fix it.
Go to Petco and buy the 10g fish starter kit, then head over to the LFS and buy 15g of water, while you're there pick up Maracyn II (fresh or salt it doesn't matter).and Jungle Labs Parasite Clear The only difference between the FW and the SW version of Maracyn II by Mardel is the SW has some B complex vitamins to stimulate appetite and more importantly the SW version has 20mg of Minocycline Activity vs. the 10mg in the FW version.
Anyway, bring that mess home, set it up, get it up to temp, check the parameters, acclimate the fish, toss in EITHER two FW tabs of Maracyn II or one SW tab of Maracyn II. Give it 24 hours, do a water change of a couple of gallons, toss in the next dose, lather rinse repeat for 3 or 4 days. You'll know when the clown is better. Also, while you're at it, pick up some Cyclopeeze and try scraping a teeny bit off to feed after the first 24 hours.
The Maracyn II will take care of gram negative bacterial infections - don't use Maracyn 1 that treats gram positive - beneficial bacteria - like the stuff that builds up in your tank to help process ammonia, nitrites, etc.
Also, while the poor guy is in QT, you can hit it with a Jungle Labs Parasite Clear - has praziquantel among other things and should take care of most internal parasites (not so sure about external parasites). I successfully dosed both the Maracyn II and the Parasite Clear on the first day w/ no ill effects to a True Perc. Lost the other two in QT because I had no idea what was happening to them.
As a side note, the 10g starter kit with the heater was about $49, the one w/o was about $39, and after you've bought them you'll have a QT you can use when you need it - also a very good idea.
Hope this helps!
