yeah, i'd say a year tops, consider this... the "Reef" carbon i get is specilized for saltwater, it's a little more expensive and that shit only lasts me a month in water and that's it. the dirty and things end up filling all the pores in the carbon and it can no longer absorb anymore. If you're not smelling anything any your plant is dank i wouldn't stress, but you can get big ass tubs of cheap carbon online from different fish websites: drsfosterandsmith.com is probably the best to deal with online. goodluck!