yes there are a lot of good stuff inthe water colum but the amout i kill off in by my uv will not effect my water at all ( have lots of rock and sand , also a dsb in the fuge ) so there is enough 'good' stuff in the rock and sand to take care of the tank. thats y i kill stuff int he water colum, but it's a personal pref thing. some people like uv and some dont. i love them, would never go w/o one