I would say dont worry about the UGF. I think they are terrible and just let stuff sit under the plates that cant be gravel vac'd out. A friend of mine had a UGF that i took out and there was waste and food caked on the bottom of his tank. Needless to say his ammonia levels were through the roof. My gravel vac couldnt get to it until i finally just told him to take them out.
If you keep up with your water changes and gravel vacs you would be fine. I dont think UGF really provide much of any kind of filtration other thank water circulation and moving waste and food up.(someone please correct me if im wrong).
UGF's are still one of the best if not the best all around bio-filter available.
They are inexpensive, have no special requirements beyond maintenance, if set up correctly they are silent, and move large amounts of water with little "felt current" on the tank. However: If not properly maintained they will plug. they do not plug as quickly as most other filters, but eventually they will cause a problem if they don't get proper maintenance.
Conventional flow UGf requres dilligent gravel vaccuming but then so does any tank that isn't heavily planted so it really doesn't add maintenance. RFUG (reverse flow undergravel ) is really about as maintenance free as any filter could be. With RFUG you reverse the flow, and put a sponge filter on the pwerhead to keep it from putting any mulm under the plates. the only real maintenance is the cleaning/ changing of the sponges. RFUG greatly reduces the need to vaccum your gravel.
Now as far as using one powerhead on a 55, I personally wouldn't do it, but I don't know that it would cause you trouble. The key would be what size powerhead and where you intend to locate it in the tank. The reason for the split plates ( aside from easier installation) is that UGF RFUG both work better with even flow, and the split plates require multiple sources of water flow this keeps all areas under the plate more even in water movement. If you go with one powerhead only, I would put it somewhere near center and make sure it's a pretty good size powerhead. My personal experience is that higher flow works better with UGF, but the verdict is still out on how much better. Additionally as mentioned above and mentioned by AshDavid, RFUG is far superior and will make for a nicer tank. Penguin is IMO the best powerhead for RFUG set-ups, and they have a ready made kit ( 7 or 8 dollars) that will give you the sponge you need for the reverse flow set-up.
Feel free to PM me if you need more details or info on undergravels. I haven't had a tank for many years without one and hove no intention of ever running a tank without one again. dollar for dollar there is nothing that works as well.
dave
