lee's Dual Action Foam Filters are simple, easy to install, air driven filters. The Dual Action filters provide mechanical and biological filtration. This filter is composed of open-celled foam which provides ample surface area for beneficial bacteria colonize. These bacteria break down fish waste. Sponge filtration is excellent for nursery tanks and brine shrimp hatcheries. Does not filter out medications, can be used with or without gravel, no carbon or floss required. As air is forced into the filter, the rising air bubbles gently draws water through the sponge material, and circulates water throughout the tank (air pump not included). The Triangle Lee's Dual Action Foam Filter is rated for aquariums up to 25 gallons
I love these filters. They are cheap but they do the job well. I've used these filters for every tank I have had for 30+ years. They are a great way of developing the good bacteria that break down waste combined with small water changes either on a weekly basis or bi-weekly depending on the size of your tank. They are also excellent for breeding tanks since they won’t suck up the babies. I would recommend these filters to anyone above any other filter out there.