Have you tried routing a tube from a window to your skimmer? We've seen a massive positive impact on our pH levels afterward. If simply opening a window does well for you, I'm confident this setup will have an even more positive impact. And for the price, you really can't beat it. Just ensure you're using a large enough air tube to guarantee that all the air the skimmer uses is drawn from outside. This can significantly enhance your reef's environment at minimal cost.It works great for some people.
I tried it, but in a house full of kids and animals, any benefit is lost due to surface agitation and glass exchange.
I monitor my homes CO2 level, when I keep windows open it has the biggest impact. So I know it is the CO2.