Hello Cs. Welcome

to Fish Lore. So sorry to hear your fish isn't feeling up to par. I would suggest a 50%
water change and add some Prime or Nova Aqua as a stress reliever. The water change seems to have helped the other posters fish in the thread you've provided. If it is internal parasites a medicine called Metronidazole :
http://www.drsfostersmith.com/produc...fm?pcatid=4753
Let's get some more responses before you decide to medicate though. You really have to be careful when using medications and other treatment additives as some may destroy your cycle/good bacteria.
Can you give us the reading for
ammonia,
nitrite and
nitrate just to make sure you aren't having cycling issues?
Best wishes for you and your fish.
Ken