Garlic should boost his immune system and increase his appetite. Sounds like an internal problems to me. Garlic isnt a med, parasites cant live in it and its very good for fishes digestion process's. Fine of every fish.
You could also tried some skinned peas. Im not sure if an aro would eat that because i never owned one, but peas also would clear out his insides.
You could also tried some skinned peas. Im not sure if an aro would eat that because i never owned one, but peas also would clear out his insides.