[Aquadelight]

anything that comes in contact with water in your aquarium is a potential source of the good bactiera needed for a helathy environment for fish. No different than SW. Not having a substrate dramatically reduces the surface area that can harbor the bacteria. So..... the only additional advice I would give to the above is to be very careful to not clean the filters too rigorously. If you remove too much of the bacteria, your tank will cycle again. De-chlorinators can remove more than chlorine. Many remove or deactivate nitrites, nitrates and amonia. Overuse can prevent your tank from completing the cycle.

Just as with a reef system, the entire tank is part of the living environment.