ick? or something else

[rhythm-makers]

over a year ago I picked up some fish and after two months of treatment and quarantine I introduced them into my main tank killing all but one angel fish from what appeared to be ich. A year has gone by with one lonely angle so I decided to take a sailfin tang from another tank to give him some company.
A few days later the sailfin is covered with appears to be ich. The tank the sailfin came from had no new fish for about 6 years. he did not go thru any stress from the acclamation, as a matter of fact he started eating algae within seconds of introduction. this fish is fat and healthy. I have attached a photo maybe a can get an opinion to what he actually has. also, angel has no signs of this.

 

[HumbleFish]

I think those are flukes: https://humble.fish/flukes/

A quick 5 min FW dip would confirm: https://humble.fish/freshwater-dip/

 

[ThRoewer]

I think those are flukes: https://humble.fish/flukes/

A quick 5 min FW dip would confirm: https://humble.fish/freshwater-dip/

I would agree on "flukes" or more precisely Capsalidae, monogenean flatworms.
I would go straight to treating the fish (all the fish in that tank) with PraziPro.
The Angel might have developed enough immunity against the flukes to live with them but he can still pass them on to other fish. (see Immune mechanisms in fish skin against monogeneans)
I would also strongly suggest doing the treatment in a sterile hospital tank as bacteria can render PraziPro ineffective within hours.