I agree with Fruitbat. A bio-wheel will culture bacteria quickly because of the water moving over it, but it will not stop bacteria from growing in the substrate. I had a bio-wheel and a planted tank for a short time. The plants grew nicely. I think (it's been a while!) that plants like nitrates, and the bio-wheel will not pull nitrates from the water. Only a water change (or lots of plants) can do that.