oh, also, your RO water should have ZERO nitrates, not just a little.... this could be your problem.. do you buy RO from the store, or do you have an RO/DI unit.... you might need to look for a new water source. Also, you need to clean those canisters. to clean the media, just do it with a water change and rinse the media with the water you pulled from your tank. Do this AT LEAST every 3-4 weeks, if not with every water change. it gets rid of the detritis, but doesnt kill the beneficial bacteria. Then clean the foam with HOT HOT tap water very well, then rinse in RO water.