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Reverse Flow Under Gravel Filtration


Dear Aquaworld,

I'm sure you guys get all kinds of strange questions, but I'm new and green.  I don't know what is a strange question and what is not. I want to set up my first tank.  Someone told me about a new idea that involves using a canister filter for the primary filtration, and returning the filtered water to the tank UNDER the gravel, to blow detritus and waste OUT of the sand/gravel bottom into the water, where it will be removed by the canister filter.  This sounds weird, and I don't know what to make of it.  Nor can I imagine how to set up such a filtration system.  I'm hoping you can tell me whether or not this idea is hogwash, and if it's not, offer some advice/insight.

Thanks for your time and help!


Bob Wallen
Temple Terrace, Florida, USA


Dear Bob,

The system you are describing is often referred to as reverse flow under gravel (UG) filtration.  Some people use a power head with a pre-filter attached to the intake and then pump the water under the UG filter plate.  Under gravel filtration is no longer recommended whether it is normal or reverse flow, as detritus (fish waste, and other decaying material) gets trapped under the plate.  Over time the trapped detritus will bring down the water quality, and the only way to remove it is to take the UG filter plate out.

The easiest way to filter an aquarium today is to use a hang on the tank power filter.  I recommend sand as a substrate, as it helps keep detritus on top of the bed so the filter can remove it.  If you already have a canister filter, make sure you keep up on the maintenance, as people with canister filters often don't clean them as often as they should.

Tony Griffitts