LUST HYDRO SPONGE IV HS940 80G

Most aquarium filters now use a motor to force water through some kind of filter pad which must be replaced at intervals. However, before there were reliably sealed electric motors, most home aquariums moved water using the "airlift" principle, in which a rising column of bubbles pulled water through the filtering material. This is an elegant and just about failsafe method. Debris in the tank cannot ever jam the external air pump which feeds the filter, and if electricity is interrupted, the filter cannot lose siphon, it simply starts bubbling again when power is restored to the air pump. Many fish love to play in the rising stream of bubbles.

Hydro Sponge filters, first marketed in the 1990's, are a more recent application of the airlift. Hydro Sponge IV is intended for tanks up to 80 gallons. Made of dense, strong plastic with a weighted base which holds the sponge up away from the aquarium bottom, they dismantle easily for cleaning of the sponge. The pores within the sponge provides an enormous surface area for colonization by beneficial bacteria providing very thorough biological filtration. They can be powered by an air pump with or without an airstone (using an airstone will give finer bubbles and make less noise), or with an electric powerhead for those with larger tanks or who simply feel the need for more energetic water movement.

It is difficult to imagine such a simple device working well. Surprisingly, they are excellent, and can be used as the only filter in the tank for many applications. I've used them on tanks sized from 10 gallons up to 75 gallons, always with good results. The local fish store where I shop has an expensive trickle filter for their dozens of tanks, and every single freshwater tank also has a Hyrdo Sponge or similar sponge filter as well. Apparantly the sponge is doing something which the trickle filter doesn't?

Maintainence is as simple as the filter. When you perform your periodic aquarium water change, (20% every week) save some of the old water in a bucket. Separate the top and bottom parts of the filter and remove the sponge from the tank. Squeeze it out in the bucket. See all the stuff which the sponge removed from the water? Reinstall the sponge and refill your tank. Go have dinner with the money you saved not purchasing replacement filter cartridges.

In sum, a clever and elegantly simple device which works very well.