Schuran Jetstream 1. A totally unique design that prevents airlocks. The gas/water separator recycles the C02, and the intake for the recirculaion pump is oriented in a fashion that prevents gas from being aspirated. This Reactor can disolve one fill per month if needed.
The key to this reactor is a high effluent rate (>80 ml/min), and the reactor must be roughly level with the sump. It comes mounted on a piece of MDF. Customaquatic.com sells them.