The difference between an under-gravel filter and a Plenum also a dirt-magnet and a sponge-filter.

The difference between an under-gravel filter and a Plenum. It’s like knowing the difference between a dirt-magnet and a sponge-filter. Roland Wilson • 17 minutes ago (edited) Seems like people in the U.S. aren’t giving you a lot of credit to use an anoxic filtration system but rather stick to buying expensive biological media. I’m one of those folks, but I did give your system a try on my 125-gallon by using two BCB bags in my sump with other biological media. My results have been very positive on lowering NO3 and fish behavior. “If it’s not broken why fix it” works for now on this tank. Tank is running just freaking great will not change a thing. • 12 hours ago It sounds like to me you are using an under-gravel filter with lots of gravel and sand on top using no or a small air stone in like under the void under the UGF is that all it is