Oh Ok I know what your talking about. I used one when I first started but took it out after a couple of days. Package said when it was saturated it would release it back into the tank. Is there a way to tell when it is loaded other than waking up and finding my nitrates back to 180+? Is absorbtion resin the same thing. I have that in the sump on top of the bio-balls. Is the nitrate sponge regeneratable like the resin?