It consists of an acrylic tube with a stronger pump (220 gph), it has a stronger venturi recirculating and collection system for undissolved CO2, it holds about 1.5L of media. The unit can be used stand alone in a sump like this or placed inside the included Comline box for use with other in tank Comline components, we also made a second stage which can be added for greater performance, in this case it is run a bit rich on CO2 and the effluent percolates over another 3L of media. It will cost about $280 without the second stage which I think is about $80.