Also you will probably have to perform more water changes untill the tank has been running a while and the bacterial colonies are well taken. That is another disadvantage of not using filter media.......lower numbers of benificial bacteria....but probably only for the first couple months of the tanks life. I test my water every other week, and I havent performed any water changes or any other type of maint. on my FW tanks, except adding fertilizer for the plants in almost 3 months.