you can treat the fish for internal parasites by treating the water.
ingesting the them is better but many of the meds will be get introduced thru a bath..
the fish run water past their gill and will absorb meds this way.
angels are prone to camillanus worms.
I use prazi, metronidazole and levamisole Hcl
they will stop eating and can survive for weeks..yes weeks(3 in this case)
I recently had a bout with internal parasites in my wild peruvian scalare tank..two of the fish stopped eating.it too treating the tank thru 3 med cycles then the angels began to slowly take food in..some was getting spit out..I then began treating the food.(if they take the food in and spit it out they will ingest meds)
med cycles may include dosing the tank for 48 hrs..then doing a water change..in 24 hours redose the tank.
the angels are now eating with a enthusiasm.
the idea with dosing the water is to get the meds into the system..they will begin to eat.
BTW, this is no guarantee..I have lost angels to parasites..but the med treatment is effective..the angels I lost died from infections created from dead worms that were not passed.