Marineland Rite-Size Cartridge H - 12 Total Cartridges (4 Packs with 3 per Pack) 12 Total Cartridges (4 Packs with 3 per Pack) Marineland Rite-Size Cartridge (Size H) Fits Eclipse 2 and Eclipse 3 Inside the cartridge, a patented ribbed backing ensures the even distribution of activated carbon to deliver maximum Designed specifically for horizontal placement in our extensive selection of eclipse systems Color coded packaging ensures fool-proof cartridge selection