Yea people really under estimate how much CO2 is in their homes and how quickly the media gets exhausted.
That said, if you run an air line extension from you skimmer to the outside air somehow you will see cheaper and almost the same results.
For instance, my tank pH fluctuates throughout the year depending on season. During the spring/summer/fall months when I can open up the house and vent the CO2 my tank has proper pH of 8.1-8.3. However, in the winter months I cannot open the window the pH goes from 7.8ish to 8.05 max. And please keep in mind this is with me running my skimmer using fresh outside are all the time. If I were to take the fresh air off the skimmer the pH would drop I'm sure.