There is an article at the Barr Report about adding dual venturi to the CO2 reactors! Maybe that can be modded into this one!I'll wait for you to figure out how to DIY an air purge on the top!
Dual venturi DIY External CO2 reactor
This unit cost about 20$ due to using Clear PVC housing, you can use solid 2" pipe if you wish. You can find all the parts at any Orchard Supply Hardware or Home Depot. Two: 2" slip to 1/2 threaded bushing Two: threaded 90 elbow 1/2" barbed About 10 Bioballs if desired 12" of rigid...
barrreport.com