You don't give us much information about your system.
Quite often the symptoms you reported are either a water quality issue or other issues that have led to a bacterial infection. There are other possibilities to what might have brought this on. But they do all have something in common: The common things all these fish have is that they went into your tank, under your care.
This sometimes happens when aquarists rush things and put fish in their tanks too soon. Ideally a tank needs to age a few months even though the ammonia and nitrite levels are good. But there are plenty of things that could be amiss, as well as a group of microbes that can bring this on.
If you'd like more help we'd normally need a photo. Since you don't have access to this, presumably, then you'd need to let us know more about your system. We'd need to know the following about the system and the livestock:
How old is your tank? When did it originally cycle?
What kind of system do you have (tank volume, dimensions, bio-filtration method, the equipment you use, any carbon or other chemical filtration, kind of substrate, etc.).
List all specimens & sizes in the tank (fish, inverts, corals, clams, snails, crabs, shrimp, etc.).
If you have a refugium and/or sump, what is living in it?
Do you use a quarantine tank and procedure?
Foods you use and feeding schedules.
How long have you had this fish? If the fish was recently acquired (4 weeks), two more questions: Do you know what sea/ocean it came from? How did you acclimate it ââ"šÂ¬Ã¢â‚¬Å“ what procedure?
Do you use any vitamins? Fat additives? Any elemental or other additives? Please list all.
Chemistries ââ"šÂ¬Ã¢â‚¬Å“ please give actual numbers (Ammonia, Nitrite, Nitrate, Phosphate, Silica, Ca, Alk., and any others you have)
Water parameters ââ"šÂ¬Ã¢â‚¬Å“ please give actual numbers (pH and your pH range, salinity or sp. gr. & range, temperature range)
Do you see any of the following in your system: hair algae; micro algae; cyanobacteria growths; dinoflagellate (zooxanthellae) growths; brown algae; diatom growth; slimes; colored patches on rock or substrate; etc.?
Water changes (how much and how often). Kind of artificial salt youââ"šÂ¬Ã¢"žÂ¢re using. Kind of source water you are using? Have you analyzed your source water for the above chemistries? When did you do these tests last? What is the TDS of your source water?
List what you added or taken out of your aquarium system (living, decorations, and equipment) during the past 6 weeks.
Maintenance schedule.
