For fresh or salt water, Penn Plax Undertow Undergravel Filters function like a natural ecosystem, providing even filtration and flow through the entire gravel bed. Penn Plax filters are easy to install. Gravel-Guard prevents gravel and fish from getting below the filter plate. Fishguard keeps fish out of lift tubes. Requires either an air pump or a powerhead to operate. We recommend using one Hagen AquaClear 50 or two AquaClear 20's. This model measures 12" x 30" and will fit a 20L or 29 gallon aquarium.

You may have heard that undergravel filters are obsolete. Nothing could be further from the truth. They may be old-fashioned, but they work! In our opinion, any freshwater aquarium equipped only with a hang-on-tank power filter can greatly benefit from an undergravel filter. Those marine tank hobbyists that can't afford a wet-dry system can provide greater biological filtration by installing an undergravel filter. Undergravel filters also provide an easy way to set up a plenum (Jaubert) reef system.