how do these sponge towers really works?

[happydiscus]

I got this site from another post but i don't know what their purpose is.

http://www.angelfish.net/yabbse/inde...;threadid=2618


Can sum1 pls help

[flukes]

The pip in in the centre of the sponge, a air line is place down the rubing or a powerhead attached to the top. This brings the water through the sponge, up the tube and back into the water mass. Fairly simple but still one of the best filters IMPO. The sponge also acts for great surface area for biological bacteria.
Also good for discus as not much flow for young or fry. Also the sponge surface is a great food source for fry and young discus. Actually my adults will have a peck at it every now and then.