Trying to work that out. Some use a pump to get pressure into the reactor, other gravity depending on the setup location. Then there is the recommended recirculation loop that is supposed to dramatically increase the contact time and the process. There is a HUGE thread on RC about it. I'll post the link later.
For me I was thinking gravity out of a HOB
overflow (so if the siphon breaks I don't get wet feet), let it gravity feed to the bottom and drip from there into the sumo and skimmer. Then if I REALLY REALLY have to I can drill out and add the recirculation loop with a powerhead or something.
Everything I read it seems to have more plus than minus, though it is going to eat away your alk
and screw with (lower) your PH.
But it seems like a simple build, much like the scrubber. My main thing is I really don't want this 4 foot tube thing I'd rather go short and fat but I'm just not sure if the loss of height would negatively affect the pressure I need from the non-pumped gravity feed.
I got time to work through it, the new 90 build won't get started for another month or so.
Figured I might get some good suggestions or interesting banter on the topic.
I will tell you the results people seem to get are outstanding.. 100ppm to 0-5 in days to weeks. I'ma sucker for a pretty face so I tend to over feed and well .... hence my DIY interest.