Oh, lovely. I get another chance to convert someone to reverse flow filtration. I love my job!!!!!
But, let me first say that "layered", multiple filtration systems are far and away the best way to go. Using multiple types of filtration increases filtration and allows routine maintainance on any individual system without compromising the balance of the tank. More later.
I have more than a dozen tanks using reverse flow filtration. The principle is quite simple. Using powerheads and an undergravel filter, the flow is simply reversed from the conventional method. Instead of pulling water DOWN into the gravel, you pump filtered, oxygenated water UP through the bio-bed. This supplies the bacteria in the substrate with clean, filtered, oxygenated water. The flow is also more consistent than when using air pumps in the conventional method. The direction of flow deters substrate compaction and detritus build up. It allows the other filters, the prefilter on the powerheads and other filters, to remove uneaten food and debris.
Explaining the "layer"principle is also simple. You use a group of different types of filtration, hang on powerfilters(ex. Emperor 400 and others), internal power filters(ex. Fluval + series), canisters(ex. Magnum 350 or 360 from Marineland), and reverse flow power heads(ex. Marineland 660r or their other models, the 550 or 1140, using reverse flow adaptors). By combining these filters to filter a tank, especially larger tanks, you can perform regular maintainance on each individual system alternately, and still have ample biological filtration. Hence, less chance of ammonia spikes due to insufficient biological filtration. Gravel sweeps are less frequent, maybe once every 6 months or even less often, as I have a 210g planted tank that has not had a complete gravel sweep in over a year. It simply doesn't need it.
Where does one apply this philosophy? I would have to say, that on tanks less than 70g-90g it may be over kill. However, scaled down versions can apply to any tank 10g and above. I have 29g tanks that use reverse flow and an Emperor 280 for each tank. So, the system can be used on smaller tanks, just scaled down a bit.