Ista Glass Diffuser is for dissolving carbon dioxide (CO2) into planted aquariums. It simply connects to 4/6mm CO2 proof hose as part of a CO2 fertilization system. It has a built-in bubble counter, which for guidance purposes we suggest running at 1 bubble per 10L of aquarium capacity per minute. We recommend that you monitor the CO2 levels using an Ista CO2 Indicator (MC120) and adjust the bubble rate to suit your requirements.