There are two or more methods that can be used to purge the gas build up.
You can add a venturi loop to from the tube(say add a airline hose 1/2 way down) and run the line back into the powerhead(or filter), or set up another powerhead to purge exclusively and deposit the CO2 opposite from the other outflow direction.
This can be applied to any reactor made.
A bit off topic here.
The internal venturi is designed for micro bubbles, externals are for purging the gas build up mainly but this will improve their efficency later in the day.
Regards,
Tom Barr
www.BarrReport.com