Presumably my biological filter exists in both the filter and the substrate but which is most effective or most important of the 2 biological filters?
, it's the plants themselves. They are constantly removing nutrients from the water, providing O2
when the lights are on, AND, they also provide tons of surface area for the nitrifiying bacteria to grow on.
Second I would say the substrate, last, filter, no matter what tyep of filter you have. All my opinion, mind you.