Do you have any problems with the tank?
It appears to be simply Activated Carbon(AC) and Activated Alumina(AAl).
All tanks should use AC about 2 weeks/month, but AAl is for removing phospate(PO4) which is not that big of a problem, especially if there is some algae in the system that is being harvested by the hobbyist or eaten by the fish.
You could probably save money by buying these products separately.

Rockstarfish bought a large quantity of good AC and offers it to us at a good price right here on this MB. I might use a little AAl once a year, if that.
Edited by Mark Peterson - January 29 2010 at 12:17pm