Zoo Med's activated carbon filter media is made from the highest quality carbon available for superior absorption of ammonia waste products produced by captive nano tank fish. High ammonia levels can be deadly to nano tank fish. Activated carbon is one step in reducing ammonia in your nano tank. We also recommend weekly water changes of at least 20%. When adding tap water (after a water change) make sure you add Zoo Med's ReptiSafe to remove chlorine and chloramines.