Pool Alkalinity and pH in Los Angeles: How to Lower Both

You bring pH down on Saturday and by Wednesday it is back at 7.9. That is the classic sign of high total alkalinity: the water has a strong buffer, and the buffer pulls pH back to where it likes to sit. Fix the buffer and pH stops moving.

Alkalinity and pH are not the same thing

pH tells you how acidic the water is right now. Total alkalinity tells you how much the water resists a change in pH. Think of pH as the position of a dial and alkalinity as the spring behind it: with a stiff spring, the dial snaps back after every push.

The target ranges are on the pool chemistry page: 80–120 ppm for alkalinity and 7.4–7.6 for pH. This article covers only what to do when one or both read high, and why in this city they usually do.

Why LA pools read high

Tap water here arrives hard and alkaline, and every top-off adds more. Evaporation takes water out and leaves the minerals behind, so a pool that is topped up all summer starts the autumn with more alkalinity than it had in May.

Anything that gets splashed, aerated or run through a waterfall also pushes pH up on its own, by letting dissolved carbon dioxide escape. A pool with a spillway or a spa spillover drifts upward faster than a plain one.

Test before you add anything

Test alkalinity and pH on the same sample, taken at elbow depth away from the return, and read both in daylight. If alkalinity is inside its range and only pH is high, you need a small dose of acid, not the full procedure below.

Lowering alkalinity: acid, then air

Acid lowers both numbers together. Air then raises pH back without raising alkalinity. Doing the two in turn is how you end with a low-enough buffer and a pH that sits in range.

1. Run the pump and keep swimmers out. Wear goggles and gloves, and never mix acid with chlorine.
2. Pour in a measured dose of muriatic acid or a dry pH decreaser, in front of the deep-end return. Add acid to water, never the other way round. How much depends on the pool's volume and the strength of the product, so follow the label and start with less.
3. Wait at least an hour, then test again. Drops of a few points a time are normal; do not chase the number in one pour.
4. When pH has fallen to about 7.0–7.2, aim the returns up so they break the surface, or turn on a waterfall or fountain. Aeration drives pH back up while alkalinity stays where the acid left it.
5. Repeat on another day if alkalinity is still above 120 ppm. A large correction goes in as two or three rounds, not one.

What a shock does to both numbers

Shocking barely moves alkalinity. It does move pH, and the direction depends on the product: liquid chlorine and calcium hypochlorite push it up, trichlor tablets pull it down. If you shock often, test pH afterwards instead of assuming it is where it was.

Tablets also feed stabilizer into the water as they dissolve, which is a separate drift covered in the stabilizer guide. Rain dilutes everything at once; the order for that case is in the after-rain guide.

What happens if you leave it high

High pH slows chlorine down, so the same dose cleans less. It also lets calcium come out of the water and crust the waterline tile, and the crust gets harder every month. If you already have it, the tile cleaning page explains what removal involves.

Low alkalinity is the opposite problem. pH swings after every rain or dose, and acidic water etches plaster. Raise alkalinity with baking soda, in small amounts and with the pump running, and test again before adding more.

What it costs

Doing it yourself, you pay for the acid and the test kit, and those prices are the store's and the brand's, not ours. The amount you need changes with the pool's volume and with how hard your tap water is.

Our weekly visit includes both readings, and the technician adjusts them before moving on. The monthly price from $159 already covers standard chemicals, as the price list shows. The visit itself is described on the weekly maintenance page.

Stuck on a reading that will not hold? Send us the test result and a photo of the water, or call (818) 740-6099.