What’s interesting about your post is you say you have been treating for ick AND using a product which does not work. I would immediately jump to the possibility that he still has ick.
Ick, which definitely culminates in not eating as the gills become infested with the parasite.
Ick-x does not work, only a copper based med like cupramine our hypo.
If you treated for ick and he looks like that + does not eat......high suspicion ick still present.
I would:
Immediately put that fish in QT and lower salinity to 1.019, this will help him respirate.
Choice A:Treat for Ick or Velvet (doubt velvet)
Use cupramine or similar copperbased product.
Choice B: Treat for Ick. (This treatment requires no meds and easier on tangs)
Lower salinity to 1.009, this can be done quickly. Maintain this salinity.
Read up on Hypo.....important when you get to the part of increasing salinity...this must be real slow...like .002 max per day....
If there were any other fish in the DT, same for them.
Your DT would have to go without fish for 76 days.
Read up on both treatments.
In both cases, try and feed a little each day, whatever he is used to.
Change about 10% water every other day maintaining either the copper dosage or the salinity dependent on which, if any treatment you pick. This is to ensure no build of ammonia in the uncycled QT.
Anything treatment in the DT, or is other than copper, hypo or TTM, DOES NOT WORK.
If a fish got better using other than these documented treatments, the fish recovered on its own.
