That's absolutely not true in this case. Again, plants can use ammonia as a food source. And the bacteria that grows on the surfaces of plants can process wastes. But that does not mean the plants serve as the sole source of filtration in a planted tank. Or in this case, the OP's tank.
Not everyone is going to have an aquarium so thickly planted with high-growth plants that an electrically-powered filter is unnecessary. That's why it is important for filter media within an actual filter have time to grow and develop bacteria that can process ammonia. For example: exactly what the OP is trying to do.
In a planted tank, the plants themselves are the filter media. Thus, there is no traditional filter media to be established.