When I used Acriflavine I treated for 3 - 5 days as per instructions. This is not the best choice if you keep plants and it will kill most if not all of your BB. Before treatment save some Bio-media in another tank to use afterwords so you don't have to compleatly re-cycle the system.
Another, maybe better alturnative is to use it as a bath. In a seperate Hospital tank, with an air stone use 38 mg per gallon of water. After 2 hours, return fish to the main tank. This is perfered if possibile because of the effect it will have on the main tanks Bio-filter.
Acriflavine may also be used as an alternative to Malachite Green if you keep species sensitive to it.
Activated carbon will remove the drug from the tank. After treatment do as large a water change as possibile, filter with carbon for about three days and the drug will be completly removed the system. Acriflavine is sensitive to strong light and UV so you should keep the tank dark during treatment. Water with a Ph below 7 (acidic) also decreases it's effectivness.
Hope this helps. What are you trying to treat?