So, it's been a month since the last modification to my scrubber set up and here's what I've discovered...
Drawing air from the outside is only marginally better in my case due the the chronic idling of delivery trucks in the street directly below my apartment. Also it drops the temp of the tank too low at night.
For the past 4 weeks I've been drawing air from inside the apartment into the scrubber via the smaller of the two available SuperLuft pums on the market. It enters the tank via a large pond sized air stone in the sump.
The air stone makes a significant difference by better diffusing the scrubbed air into the water. I'm also dosing 1-1.5 gallons of kalkwasser solution per day. Generally I'm able to maintain the tank around 8.20-8.15 during the day and 8.05-8.10 at night.
Obviously the newer the soda lime the better my results. I find that I need to change the soda lime about once a week even before it fully turns purple. In my experience pH stability has been a better indic
ator of when to change the medium than when it changes color.
The scrubber alone won't do it for me and I find the kalk essential. When I've dosed 2 part instead the tank has been less stable. So it's a combination of the scrubber, air stone and kalk that makes this work for my particular situation. Remove any one of these variables and the tank becomes unstable.
A side bummer of elevated CO2 has been my amazing ability to grow nuisance algae. The kind nobody wants to eat. I'm working on growing more grape calurpa in the refugim to try and reduce the CO2 even further. I hate the stuff because once you put it in the sump it roots itself in every nook and cranny of the live rock. Personally I prefer chaeto, but it doesn't grow very well in my sump.