Sponge filters are one of the most economical and easy to use/maintain filters in the aquarium/aquaculture hobby. 
The AquaTop sponge filters offer excellent filtration while oxygenating the water. You simply can't beat the price and performance of the CAF Series which can be used as a stand-alone filter, a breeding filter or for extra biological filtration in heavily stocked aquariums. Even add it to your external or top filters as a pre-filtration unit! Another neat feature of the CAF Series is the airlift system for excellent biochemical filtration and pleasantly quiet operation. The foam materials support the colonization of bacteria, allowing for mechanical and biological filtration, which will break down harmful ammonia and nitrite.