Raising alkalinity
Baking soda (sodium bicarbonate) is the standard alkalinity increaser and is the same chemical as most branded "alkalinity up" products. It nudges pH up only slightly. Soda ash raises alkalinity too, but also raises pH a lot, so use it only when both are low. Add up to about 40 ppm of alkalinity at a time.
Lowering alkalinity
- Add acid to bring pH down to about 7.2. The calculator shows how much.
- Aerate: point return jets up, run waterfalls, fountains or a spa spillover. This raises pH without raising alkalinity.
- When pH is back near 7.6, repeat. Each round lowers TA a little.
- Stop when TA reaches your target. Never let pH fall below 7.0.
It takes several days. There is no single dose that lowers alkalinity on its own without also crashing pH.
What alkalinity to aim for
- Manual chlorine with liquid chlorine or bleach: 50 to 90 ppm, often 60 to 80.
- Salt water pools: 50 to 80, because a salt cell pushes pH up.
- Pools using trichlor tablets: toward the higher end, because trichlor is acidic.
- Plaster pools: check the result with the CSI calculator.