Pool Chemistry in Los Angeles: What to Test and How to Fix It

Pool chemistry comes down to five numbers: free chlorine, pH, total alkalinity, calcium hardness and cyanuric acid (stabilizer). Chlorine does the cleaning. The other four decide whether the chlorine works, whether the water eats your plaster or coats it in scale, and whether swimmers' eyes sting.

They are linked. Alkalinity holds pH steady, stabilizer slows chlorine down, and calcium keeps water from pulling it out of the surface. Change one with no thought for the rest and you chase the readings around the pool for a month.

The ranges to aim for

These are the industry ranges for a plaster pool with chlorine. A salt pool shifts a few of them, and the salt article has its own targets.

• Free chlorine: 1–3 ppm. It kills bacteria and algae. The more stabilizer in the water, the higher this needs to sit.
• pH: 7.4–7.6. Above 7.8 chlorine slows down and scale starts to form. Below 7.2 the water turns acidic and etches plaster and metal.
• Total alkalinity: 80–120 ppm. It buffers pH so it stops swinging after every rain or dose.
• Calcium hardness: 200–400 ppm. Too little and water pulls calcium out of plaster. Too much and it settles as white crust on the waterline tile.
• Cyanuric acid: 30–50 ppm. It shields chlorine from the sun. The stabilizer guide covers how to bring it down when it creeps too high.

How often to test

Chlorine and pH weekly, and twice a week in July and August when a hot pool burns through chlorine in a day. Alkalinity weekly as well, since it is what keeps pH from jumping. Calcium and stabilizer move slowly, so once a month is enough, plus after a heavy rain or after you refill part of the pool.

Test strips are fast and fine for a weekly look. A drop kit costs a little more and reads chlorine and pH more exactly, which matters when a number sits near the edge of its range. Take the sample from elbow depth, away from the return jet, and read it in daylight.

The order to fix them in

Fix them in the order below, with the pump running, and wait at least 30 minutes between additions before you test again. Adding chlorine first is the usual mistake: if pH is high, most of that chlorine is working at half strength.

1. Total alkalinity. Baking soda raises it. Muriatic acid or a pH decreaser lowers it.
2. pH. Soda ash raises it. Muriatic acid lowers it. Once alkalinity is in range, pH moves less and stays where you put it.
3. Calcium hardness. Raised with calcium chloride. Lowering it means draining part of the pool and refilling with softer water.
4. Stabilizer. Raised with cyanuric acid. Lowered only by replacing water.
5. Free chlorine. Last, so the dose works at the pH it was designed for.

Add chemicals one at a time, pour them in front of a return jet, and never mix two products in a bucket. Acid and chlorine together release chlorine gas.

What is different in Los Angeles

Fresh water here is hard and alkaline. Every top-off in summer brings calcium and alkalinity with it, and a pool that loses an inch a week to evaporation ends the season with more dissolved minerals than it started. That is why pH in a Los Angeles pool tends to rise by itself, and why you add acid far more often than baking soda.

Sun adds to it. Chlorine burns off fast in July, so tablets feed stabilizer into the water until it passes the range. Rain does the opposite, and a storm dilutes everything at once; the after-rain guide has the order for that case. Algae on top of the problem gets its own page, because green water is a chlorine failure first and a chemistry question second: green pool clean-up.

When the water looks fine but the numbers are not

Clear water is not proof of balance. Low pH and low alkalinity leave the water sparkling while it dissolves the plaster slowly, and the first sign is a rough surface and rust-coloured stains by the steps. High pH and calcium look clean for weeks, then crust the tile line and cloud the water. If the water is already hazy, the cloudy water article lists the causes in order of likelihood.

What pool chemistry costs

Doing it yourself, you pay for a kit or strips and for the chemicals, and none of those prices are ours: they are set by the store, the brand and the container size, so check what your local pool store charges. The yearly total depends on the pool's volume, how much sun and leaf fall it gets, and how often rain or a refill knocks it out of range.

On our weekly service the full chemical panel is part of every visit: pH, alkalinity, chlorine, cyanuric acid, calcium, phosphates, TDS and salt, each adjusted to range. Weekly service starts at $159 a month, and standard chemicals are included, as the price list shows. Specialty treatments are billed separately.

Not sure how to read your numbers? Send the test result and a photo of the water, or call (818) 740-6099.