I do not know about dosage of Acriflavine but one of my Discus has Velvet. I am treating with something else for the third time in less than two weeks. I am not sure if you treat and still see the whitish spots the fish will get better without additional treatment so I re-treat. I have noticed this with other ailments. I may be treating for too long but better too long than too short. I do not know about that Acriflavine and its side effects but if there are no side effects, retreat. Does it effect your beneficial bacteria? If not retreat.