Nice tight pH range. Do you by chance have a refugium with lighting on at night in order to get such a small swing during the night?Glad to see you got it working the way you want it to with the 3-way valve. Myself I am only using a 2-way valve but my valve is very close to my skimmer compared to the CO2 scrubber. I am using the recirc method but also have outside air going to the scrubber mixing with the air from the skimmer. My outside air is drawn from the furnace fresh air intake and runs 65ft to the scrubber thru a 5/8" ID hose. One thing I like about this setup is I only have a 0.08 PH variance in a 24hr period. Like you, if I did not use a electronic ball valve my ph would approach the 8.65-8.7 mark which I did not want it to go that high.