CPR Bak-Pak Dual Pak Protein Skimmer CPR has taken the proven technology behind the Bak-Pak 2 and the Bak-Pak 2R, and created the new Bak-Pak Dual Pak. The Dual Pak provides a complete hang-on filtration unit for tanks up to 100 gallons that incorporates two proven skimmers with a biological filtration chamber in the middle. Using proven Rio Rejuvenation Venturi technology, the protein skimmers are flooded with bubbles for constant removal of excess organic. The biological chamber utilizes CPR`s Bio-Bale biological filter media to provide maximum surface area for beneficial bacteria to colonize. Simply hang the Bak-Pak Dual Pak on the back of an aquarium, plug in the rejuvenation venturi powerheads, and enjoy worry-free operation.