UG filters do in fact filter water. Water passes through the gravel which is the biological filter media. While we may agree the surface area of gravel is much lower than other medias, it works all the same

Many people overlook UG filtration even though it can be quite effiecient and cost effective. Turning your tank 12 times, I'd say is enough.

I clean under the plates by siphoning out of one tube while pushing water into another tube with a big powerhead and can clean under the plates without removing the gravel.

I'm pretty sure its not 12 times but I have to check the actual flow on the FX5 and both of the U4's to know for sure exactly.

ya but the plate between the tank and the filter makes room for crap to be there .. check out kgtropicals latestest vid on undergravel filters