treatment

Hi all, so I work at my university's wet lab. We have a 250 gal tank with two convict tangs, a snowflake eel, a toby, and a butterflyfish. Today one of the convict tangs had this weird brown spot near its tail. Any help would be greatly appreciated. I have looked around to try and figure it out...

2 problems that have been driving me crazy, could really use some guidance on best courses of action. Have a black trigger lost his eyesight due to a parasitic infection. His health is back to normal but it’s quite painful to watch him scavenge for food Not sure if euthanizing or letting him...

I added a rabbitfish to my 150 gallon FOWL tank a couple of days ago. I didn't notice it the first day, but the second day I saw it had a pink lump on its mouth. Can someone help me identify it as well as know how to best treat it? my water parameters are 0.0 ammonia, 0.0 nitrite and 0.0 nitrate...