I was reading some of the posts on how air to the skimmer affects PH. And I have had low-ish PH issues. Instead of fancy CO2 scrubbers, or big air tubes outside, I tried something VERY simple. I put a pipe on the skimmer a couple of feet long, just up and out of the fuge area. So still in the garage, but pulling air a little ways away, instead of right next to the water in the sump. Very clear difference. Not huge, about 0.1, but clear, and just from moving the intake a foot or so. Likely that it was recirculating air, being so confined, and CO2 became a bit saturated.