The AM CO2 External Reactor 1000 (BigAls aswo #15733) for $62.99 . Could of went to Lowe's or Home Depot and made the same thing for about $15 but to dang lazy. Now if only I can get my check valves to work. I have two on now and I am still afraid to turn of the CO2. (don't have solenoid on yet). First time I turned it off with only one check valve (probably in the wrong place) my bubble counter flooded. I think I will wait and work on it more tomorrow, too dark to see tonight
. (by the way, my husband was VERY helpful in putting the reactor on, did it all by himself!)