pH
Last reviewed August 11, 2026
Dosing
In 15,000 gallons, 12 oz of 31.45% muriatic acid drops pH 0.2. To go the other way, 6 oz of soda ash raises it 0.2. Dissolve soda ash first and spread it over the surface. What to buy and what to carry: starter chemicals.
- Pour acid into the deep end with the pump running
- Never pour acid into a skimmer
- When you dilute, acid goes into water. Never water into acid.
- Retest after a full turnover, not five minutes later
pH decides how well everything else in the water works. Chlorine gets weaker as pH climbs. Plaster etches when pH drops. And pH moves the LSI more than anything else you can change in one visit.
Which way it drifts
| Pool | Drift | Why |
|---|---|---|
| Plaster | Up | New plaster gives off calcium hydroxide |
| Salt | Up, hard | Making chlorine from salt raises pH. You'll run acid more often. |
| Vinyl | Fairly steady | No plaster to leach. Watch the low end instead. |
| Water features | Up | Waterfalls and jets drive off CO₂ |
If pH climbs every week on a plaster pool, check total alkalinity. High TA pushes pH up and keeps pushing. Dose acid all you want, it comes back. Bring the TA down and the pH problem goes with it. See total alkalinity.
The vinyl floor
Don't take a vinyl pool under 7.2. Low pH pulls the plasticizer out of the liner. It gets brittle, then it wrinkles, then it splits at a seam. No amount of chemistry brings it back, and a new liner is a four-figure conversation with the homeowner.
pH and LSI
pH goes into the LSI calculation one for one, which makes it your fastest lever. On a hard-water pool you can't do much about the calcium, so holding pH at 7.4 instead of 7.6 is often what keeps the water balanced instead of scaling. See reading the LSI.
Logging chemistry on every stop? PoolSpartan keeps the readings, works out the LSI as you type them, and sends the customer a service report when you close the visit. Free to start. We only get paid when you do.
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