It's not the oxygen but lower concentration of CO2. Adding more oxygen will not lower ph, but adding less CO2 will.Pretty funny you say you dont know how it works then correct me lol. FYI when i mention oxygen it is related to the ratio of co2/oxygen levels in the air. So while technically high co2 is a depresser of ph introducing highly oxygenated air (ie less co2) drives ph up (assuming the tank has high co2 levels). And knowing the scenarios of when it works and why really is not that complicated. Even getting to the chemistry is not that complicated. As someone who knows very little about chemistry I manage to understand it.
Here is a good article. http://www.reefkeeping.com/issues/2004-09/rhf/
The question is, does my skimmer add enough air to make a difference?