Windows open can be much more effective than outside air to a skimmer because the skimmer plan leaves the whole tank top and possibly other means of aerating the tank with the likely high CO2 indoor air.
That said, outside air or scrubber air to a skimmer has certainly helped many folks.
This article describes my aeration test to distinguish if you just need more aeration (uncommon but possible), or if you need outside air:
pH And The Reef Aquarium
http://www.reefedition.com/ph-and-the-reef-aquarium/
The Aeration Test
Some of the possible causes of low pH listed above require an effort to diagnose. Problems 3 and 4 are quite common, and here is a way to distinguish them. Remove a cup of tank water and measure its pH. Then aerate it for an hour with an airstone using outside air. Its pH should rise if it is unusually low for the measured alkalinity (Figure 2). Then repeat the same experiment on a new cup of water using inside air. If its pH also rises, then the aquarium’s pH will rise simply with more aeration because it is only the aquarium that contains excess carbon dioxide. If the pH does not rise in the cup (or rises very little) when aerating with indoor air, then that air likely contains excess CO2, and more aeration with that same air will not solve the low pH problem (although aeration with fresher air should). Be careful implementing this test if the outside aeration test results in a large temperature change (more than 5°C or 10°F), because such changes alone impact
