A real honest to God Live Deep Sand Bed full of bristle worms, microcrustaceans, aerobic/anaerobic bacteria, variuos other worms/critters does not need an UGF and will work better w/o one.
A sand/CC substrate that contains bacteria to convert ammonia to nitrite to nitrate does not need an UGF. In this sense ALL CC or sand will eventually be alive.
An UGF using fine sand will probably not work at all.
An UGF with CC can become a Nitrate factory if not properly maintained.
[ October 03, 2001: Message edited by: fender ]