Aeration
Also called: aerating, outgassing.
Aeration is breaking up the pool's surface so dissolved carbon dioxide escapes, which raises pH. Aeration is the only way to raise pH without raising total alkalinity. Fountains, bubblers, deck jets, spa jets, spillovers and return jets aimed up all aerate the water.
Why it matters
Run water features a lot and your pH climbs faster, so you add muriatic acid more often. Nothing's wrong; that's the feature doing its thing. You can also use it on purpose. To lower total alkalinity, add acid so both pH and TA drop, then aerate to bring pH back into range while TA stays down, and repeat. Aeration also burns a little more chlorine and cools the water by evaporation, which works best on clear, breezy nights and is muted in high humidity or under a screen enclosure. Lowering alkalinity toward 60 slows the pH climb.
In numbers
Want to raise pH after adding acid? Run a bubbler for a day.