The ViaAqua Acro-cal Calcium Reactor offers a simple and convenient solution for maintaining calcium and alkalinity in your reef tank. After the initial setup, the calcium reactor requires minimal maintenance. A calcium reactor is almost a necessity for tanks heavily stocked with stony coral where calcium and alkalinity demands are high and will promote coral line algae growth. Calcium reactors provide a steady supply of calcium by using CO2 to dissolve media in the reactor and, thus, releasing calcium into your water. The effluent released also acts as a buffer to stabilize kh. Not included, but necessary for use, are a CO2 System and reactor media.Features:Built in water pumpFor use in sump or as a hang-onComes with bubble counterEasy to remove twist-off topFor aquariums from 10-75 gallonsBuilt in bleed valveDimensions: 14-3/4" H x 3-7/8" W