The AquaClear AC20/30 Clear-Carb Insert Value combines the benefits of Carbon and Clearmax for fresh and saltwater aquariums. It eliminates odors, discolorations and impurities, while controlling phosphate, nitrite and nitrate to produce crystal clear water. For the AquaClear AC20 Power Filter and AquaClear AC30 Power Filter. The Product Manual recommends you replace the the Clear-Carb Insert every month. 1-pack.