If I understood your tubing correctly, isn't this design very wasteful for the media? Looks like your Y feeds into the scrubber and takes both skimmer cup air (recirculating) or outside air (high co2) so what the system is doing is when pH is under 8.3, solenoid closes so it recirculating. This is very efficient on removing co2 and preserving the media bc effectively you are only scrubbing in-tank co2. When it goes over 8.3 it opens and you are sucking in outside high co2 air but its still going to the scrubber so you are basically relying on the inefficient method to let some co2 thru to lower ph under 3. This is both an ineffective method of lowering pH by increasing co2 (bc its still going thru scrubber) and also an expensive method bc you are burning thru the media.
This, by putting the solenoid on the other side, you avoid the weakness of the current design and is generally more effective. When 8.3 goes above 8.3, the solenoid will bypass scrubber so you save media and can bring down the pH much faster then it will resume recirculating .
If you are recirculating you dont need to add more water, the skimmer air is humid enough. If anything, on the skimmer to scrubber in tube, you should have a moisture capture instread bc the problem is often too much moisture going into the scrubber