Join Date: Apr 2007
Location: HI, but Pueblo, CO for now
You don't need that extra hole on the top but it does help. It makes priming the reactor a whole lot easier. Also, you can tee that line off and recirculate the built-up co2 gas. You can either have that line go to a powerhead and have some mist go into your tank or back to the pump/filter powering your reactor. I usually do the mist option myself.