The CPR Aquatic Bak Pak Combo Protein Skimmer Pre Skimmer/Bubble Trap Box works with the CPR Aquatics Bak-Pak 2R+ Reef Ready Protein Skimmer and the CPR Aquatics Cyclone Bak-Pak 2 Bio-Filter Protein Skimmer. The Pre Skimmer/Bubble Trap Box will help ensure you get the dirtiest water off the surface while reducing the bubbles released back into the tank. The Box attaches to the powerhead.