Gang@Ukaps. I am currently using a Dennerle Flipper for my co2 - the gas enters at the bottom and climbs a series of ladders, as it climbs the ladder the bubbles get smaller and at the top of the system there a collector at the top of the flipper to collect waste gases. Dennerle Quote: Mode of functioning: The CO2 supplied by the CO2 fertilizer system is released from the opening at the bottom of the Flipper. The CO2 bubbles then rise slowly along the channels in the Flipper. As the bubbles rise, the CO2 dissolves in the aquarium water - the bubbles thus become visibly smaller as they progress towards the surface of the water. Waste gases are separated from any residual CO2 in the collector and discharged automatically. I would like some advise on changing to a new diffuser as this one is an eye sore - bit I don't know which one to buy, my tank is an Aqua one AR980 approx. 217 litres. Regards Paul.