The sponge doesn't need replaced, like filters in freshwater tanks. Yes, the bacteria would grow back if he bought new ones, but that would get expensive. I doubt he really needs it for biological filtration (he stated he used it for mechanical) as the live rock and sand do the biological filtration, not to mention the protein skimmer. Taking clear water, and turning it crystal clear. The only flaw I found with the aquaclears is the plastic is thin. I have 4 broken ones in the basement. Wish I could use them though. Lost all the U-tubes for mine.