If you are feeding the reactor just via a siphon, then a few feet of head pressure is necessary. If you are using the original design where the circulation pump helps to suck in water then less head is necessary. I never found either to work all that well which is why I now use a MasterFlex. I don’t recall the exact hose configuration on the mini, but on the pro I just used the original CO2 vent to move effluent to the secondary chamber thus eliminating gas buildup in the main chamber.