When the roots of plants grow into the plastic under gravel filter, it would be tough on the plant to move it for say- cleaning or
Under Gravel Filters collect crud at the bottom of the tank - with nowhere for it to go until it's time to empty the whole tank for cleaning.. Check into canister and HOB (Hang On Back) filters to make life easier!
Actually, you can do it. My 20 gal TV tank has been setup for 2 years. It is heavily planted and has a UGF. Now I set this up before I had a Clue, but it still works fine. Plants do well. Water still appears to flow through the UGF.
I would not do it now, as I have learned a few things. But I aint tearing it down either. "If it aint broke, dont fix it" Right?
Another thing you can consider with a UGF is to have plants that don't root in the substrate. There are lots, like java moss, java fern, bolbitis, anubias, that you can attach to things. If you have the ornaments anyway, why not dress them up with real plants.
My experience was like Shiftaltumlock's, though my UGF plate is in storage now. Unnecessarily complicated, IME. The UGF was meant to encourage a slow percolation of water through the rootzone, not fast enough to blast a lot of oxygen all through the gravel. Hooking up a powerhead ruins an UGF. So does vigorously scouring out areas of your gravel with vacuuming.
The accumulation under the plate is humus, though it's often thought of as "dirt." It can be removed by putting a siphon down the riser tube.
There's more rant along this vein at www.skepticalaquarist.com in the set-up folder, under "Mis-Tech" at the bottom... see if you agree.
I too have a heavily planted tank with a RFUGF. Here's the trick: One third of the tank is RFUGF with a foam pre-filter, the other 2/3 have a plantable substrate under the gravel. Best of both worlds. Also, my DIY CO2 bubbles feed directly into the tube between the pump and the UGF plate. As far as I can tell, I am getting 100% diffusion of my CO2.
Matak, that's a fresh set-up concept for me! What size is the tank? I picture it that your UGF filterplate is a single plate that covers 1/3 of the bottom, covered with regular aquarium gravel? at one end of the tank and then an enriched substrate with a gravel top layer, heavily planted, fills the rest of the tank. Is that right?
Then your bubbled CO2 is carried down under the UGF plate and gets pretty completely dissolved in the unplanted section of gravel. And the rooted plants get the benefit of a low-oxygen zone where iron and phosphate are freed from the substrate?