Hydro Logic BIGboy Green Coconut Carbon Filter (HL22006)The Hydro Logic 20" X 4. 5" Replacement GreenBlock Coconut Carbon Filters are made using high performance coconut shell green carbon which has more micro pores compared to other types of carbon and features a unique binder system delivering a product with superior absorption capacity and kinetic dynamics. Use this to replace your carbon filter for the Hydro Logic Big Boy filtration units.