Give the angel a
FW dip for at least three minutes but no more than five. Make sure the temp is close to the tank temp and of course dechlorinate it first. Use
RO water if you can.
While the angel is in the freshwater, watch to see if anything falls off, particularly if it is opaque white and round. If you have a hospital tank, put the angel in it.
What other fish live in there with the angel? The ragged fins may suggest the angel is getting picked on.
Some info. on this parasite...
There is a particular external parasite that is known to be problematic for the fact it cannot be killed with medications...not even copper can touch it. The only way to kill them off the fish is to dip the fish in freshwater. I'm still looking for the name of this parasite, but I do know it's a trematode of sorts. The parasite is natural to the lumberjack fish Japanese fisheries harvest. When these fishermen started trekking these fish around the world, they spread their parasite too and now the parasite is found in almost all the oceans.
It is nearly impossible to see these parasites. They are transparent and round. When exposed to
FW, they turn opaque and fall off the fish. A cloudy eye can suggest these parasites may be present. It's the only place on the body of the fish they show up.
Angels are one of the fish that are common to have these parasites. Many fish are so it's a good idea to dip most new fish before purchasing if possible. Some fish should not be
FW dipped like wrasses and small gobies. Tangs, angels, butterflies, damsels, triggers, puffers, lions, groupers, anthias, etc are all OK to dip. Even eels, but not right after they eat.
If you see these parasites are present, then I would suggest to treat the angel with an antiseptic and Formalin. Aquarium Pharmeceuticals use to have Wound Control. They might not have it on the market anymore. I don't know if they had substituted it with another product. It went on the fish directly instead of in the tank. Good antiseptic.
You will want to dip the angel again. These parasites are monogentic which means they do not need a second host to complete their life cycle and breed right on the fish.
Let me know how the dip turns out...and I will warn you now...some people may not condone doing
FW dips but it is the only way to rid these certain parasites and a positive way to confirm or deny the presence of these parasites. It's worth the stress the fish goes under for the moment. If the angel lays down just fan water over it's gills. The fish will be fine. I've dipped hundreds of fish without problems from the dip.
I notice you have a 36 gallon tank with a yellow tang. Too small of a tank for it and being that and having very close quarters with the other fish, you may want to dip them too. Again, please let us know what other fish are in there.