It is very hard to tell when ammonia is 0 and nitrite is 0, but nitrate is also 0, usually, nitrate is round 10-20-30. Are you sure the test result correctly, have the water been cycle?.........
I also have a bannerfish, and it is very active. The bannerfish is a hardy... I would test the water again, also take it to the LFS to double check if their result and yours are the same......