Marineland Penguin 375 Bio-Wheel Power Filter

The Marineland Penguin 375 is the large hang-on-back filter in the Penguin line, made for aquariums up to 75 gallons. It runs water through mechanical, chemical and biological stages. Its signature part is the Bio-Wheel, a pleated wheel that turns in the outflow and spends half its time in air.

How the Bio-Wheel works

Beneficial bacteria need oxygen to turn ammonia and nitrite into nitrate. As the Bio-Wheel spins, the bacteria on it are exposed to air and water in turn. Marineland calls this wet/dry biological filtration. Because the wheel holds its own bacteria, you can change cartridges without wiping out the biofilter.

Cartridges and flow

The filter uses Marineland Rite-Size C cartridges, which handle the mechanical and chemical stages. Flow control lets you adjust output up to 375 GPH. Turn it down for slower fish, or leave it up in a heavily stocked tank.

The Penguin family

Penguin filters come in six sizes: 100 for tanks up to 10 gallons, 125 up to 20, 175 up to 30, 275 up to 50, 375 up to 75 and 450 up to 90. For a smaller tank, see the Penguin 200.

Keeping it running

• If the Bio-Wheel stops turning, lift it out, rinse its axle area and check for debris.
• Keep the water level high so the outflow doesn’t splash.
• Swap cartridges on a regular schedule and rinse the intake.

Who should look elsewhere

If you want to build your own media stack instead of using cartridges, an AquaClear 110 or a canister filter gives you more control.