Protein skimmers can be a great tool for fighting chronically low pH problems. They inject air into water while at the same time blowing off excess CO2 from the aquarium’s water. Sometimes though, the effectiveness of the protein skimmer’s ability to draw in air can further depress CO2 if the surrounding environment also has excessive amounts of carbon dioxide present. To remedy this, some hobbyists run the air tubing from the skimmer all the way out of a window. This allows the skimmer to draw in fresh air and provides the most effective way to stabilize or even raise aquarium pH.