I have a 7'x2'x2' aqurium holding a merodontotus tigrinus,green arowana,some clown loach and 4 large gold severums.
The severums fins are feathery a bit like fin rot but not as severe.
one also has developed an ulcer type wound on her side.

I think protozin is the cure but can it be used with the merodontotus at half doses?