Ive seen ot of people using solenoids to control their ph.... i decided to try it with an electronic ball valve which did help some. But when the valve is open and drawing fresh air. It does still draw a small amount of air through the scrubber. I just found and set up a 3 way electronic ball valve which will block the flow completely through the scrubber when drawing fresh air. I found this would be easier then having two valves (one goes on when the other goes off) will keep you posted if this works better.