What Causes Aeration?
Aeration happens anytime bubbles or ripples form in the water.
Aeration can occur from:
- Splashing
- Spa spillovers
- Waterfalls
- Sheer descents
- Bubblers
- Fountains
- Return jets flow pointing up
- Rain
What Causes Aeration to Raise pH
Anything that increases the surface area of the air-water interface increases the rate of carbon dioxide leaving the pool water.
Pools are intentionally over-carbonated both to provide a pH buffer and to saturate the water with the carbonate portion of calcium carbonate to protect plaster surfaces from dissolving. In other words, there is a lot more dissolved carbon dioxide in the water than would naturally occur in equilibrium with the air (though obviously not as much as a carbonated beverage!).
As for why the pH rises, the easiest way to explain it is that some of the carbon dioxide in water is carbonic acid -- that is, carbon dioxide plus water makes carbonic acid -- so removing carbon dioxide is like removing carbonic acid. Removing an acid from the water makes the pH rise.[1]
The best way to raise pH is by aeration of the water. That raises your pH gradually while not affecting your TA.
