I actually think you’re probably dealing with flukes (based on areas of color loss and the fins being tattered) although a bacterial infection is certainly possible. I reconmend a freshwater dip in a dark bucket. Match temp and PH if possible.
If you see “sesame seeds” come off, and I’m pretty confident you will, treat with Prazi pro twice, 5-7 days apart. This can be done in your display and in fact should be due to the fact other fish have them also.
If you remove to quarantine you can treat with general cure instead. If there aren’t flukes I suspect bacterial infection as well which should be treated in either NFG in quarantine (first choice) or the “trifecta” which is kanaplex, metroplex, and furan 2. Again, in quarantine.
Also that fish has severe HLLE it appears. However with bad fluke infestations HLLE can look much worse than it is. This can be “treated” with time and the following:
1) high quality (clean) water
2) soaking foods in zoecon and selcon
3) avoiding dusty carbon use (rinse very very well)
4) check for electrical current in the water and if it is there, remove it.
5) feed nori, lots and vary food offerings.
This will take time, focus on what I suspect is flukes ASAP. Do the freshwater dip ASAP.
@HotRocks has a couple angels of mine right now that flukes caused what looked like severe HLLE that’s cleared up almost entirely since treating for flukes. It was crazy!
