FWIW, for many years common sense and common practice lead us to believe the undergravel filter is the best way to go for exactly the reasons bassandgrass stated. For years there was no test data on that theory other than the fact that they appeared to work well. Now every study (and there are now thousands) on the reality of underground filters is that this not to be the case. The water actually only "flows" through a few small passages in the gravel and clogs easily, that's why they need to be vacuumed often. With the new Wet/dry and other bio-technology, far larger and more effective bacteria colonies are formed and continually replaced to provide superior nitrification than their undergravel counterparts. The "fluidized bed" sand filters offer by far the largest amount of surface area for the bacteria to grow on, and the constant "bumping" of particles knocks off dead bacteria and alows new groth to take place----eliminating the need for cleaning and greatly reducing the need to change the water. One pound of sand replaces over one hundred pounds of gravel with less maintenance required. Granted, you WILL still get an anarobic, stinky gravel bed, but that is part of a natural ecosystem and not always bad.
I have over 200 inches of tilapia in my 55 gallon tank with only 2 small "bio-wheels and over 600 inches of bluegill, catfish, and FH minnows in my 150 gallon tank. I only have to change the water every few months unless the fish slow on feeding.
Last edited by Rainman; 12/07/08 09:55 PM.
