It's best to have a deep substrate with planted tanks. UGF's require a shallow substrate. If you use a thick substrate, there's a possibility that you will have gaps in the flow through the gravel.
Also, UGF's need to be maintained properly. Thorough gravel vacs need to be performed. Otherwise, detritus collects over time underneath the UGF plates. Have you seen your filter hose? Imagine that stuff underneath the UGF plates. All the detritus that collects will eventually cause dead spots and gas pockets.
As mentioned, the roots could get attached to the UGF plates and may cause the UGF to shift/move when removing/rearranging plants.
Last edited by crazie.eddie; 01-20-2008 at 09:19 PM.