This Bundle includes two items: an IceCap CO2 Scrubber, Medium; and the IceCap Color Changing CO2 Absorbent Media, 1 kg. Why do you need this CO2 Scrubber? The pH in a reef tank should be around 8.3 for optimal coral growth. If you're struggling to maintain pH, or if your aquarium suffers from chronically low pH, connecting an IceCap CO2 Scrubber to the air intake of your protein skimmer is a great way to increase and keep your pH level within ideal ranges. Tubing not included. 1 kg of IceCap Color Changing CO2 Absorbent Media is included. We also include 1 kg of media for replacing your Media in the future. Body Diameter: 4". Footprint: 4.5" X 4.5". Height: 9.5". Includes hang-on bracket.