Alkalinity buffers pH moves, so doses are estimates by design — add a step, circulate an hour, retest. Pre-dissolve in a bucket of pool water to avoid clouding.
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The dose math
soda ash ≈ 6 oz per 10,000 gal per 0.2 pH rise (side effect: each 6 oz/10k also adds ~5 ppm alkalinity)
pH chemistry is buffered — the same dose moves a low-alkalinity pool a lot and a high-alkalinity pool a little, which is why every serious dosing chart says "retest between additions" and so does this one. The steps sized above keep any single addition too small to overshoot badly.
A worked example
A 15,000-gallon pool at pH 7.0 heading for 7.5: roughly 22 oz of soda ash total — call it 2¾ cups — added as three ~1-cup steps with an hour of circulation and a retest between each. The same pool at 60 ppm alkalinity gets different advice: fix alkalinity first, because the baking soda dose will drag pH partway up on its own.
Why pH keeps sliding down
Trichlor tablets are the usual suspect — they're acidic by design, and a summer of tabs quietly eats alkalinity and pH together. If that's your sanitizer, expect this dance seasonally and keep both this page and the muriatic acid calculator (the other direction) handy. The LSI calculator shows where your water lands once everything's balanced.
Frequently asked questions
What raises pH in a pool?
Soda ash (sodium carbonate — sold as 'pH Up' or 'pH Increaser') is the standard. Borax works too with less alkalinity side-effect. Baking soda is the wrong tool here: it mostly raises alkalinity and barely moves pH — that mix-up wastes more pool-store money than any other.
How much soda ash do I add to raise pH?
The working rule: about 6 oz of soda ash per 10,000 gallons raises pH roughly 0.2 (from a 7.2 start). It's not perfectly linear — alkalinity buffers the move — so the safe play is dose, circulate an hour, retest, repeat. The calculator sizes each step for you.
Why is my pool's pH always low?
Usually one of three: trichlor tablets (they're acidic — every tab nudges pH and alkalinity down), low total alkalinity leaving pH unbuffered so it swings on anything, or fill water that arrives acidic. If alkalinity is under ~60 ppm, fix that FIRST — pH won't hold otherwise.
Can I swim after adding pH increaser?
Once it's fully dissolved and circulated — typically 30–60 minutes with the pump running. Soda ash clouds the water briefly if dosed heavy; pre-dissolving in a bucket of pool water avoids most of it.