How the calculation works
pH is not a simple dose, because alkalinity buffers it. The same acid moves pH further in a pool with TA of 60 than in one with TA of 140.
The working figures are about 5 fl oz of 31.45% muriatic acid per 10,000 gallons per 0.1 pH, and about 3 oz of soda ash per 10,000 gallons per 0.1 pH, both at an alkalinity of 100 ppm — scaled up or down in proportion to your actual TA.
Worked example
A 20,000 gallon pool at pH 7.9 with alkalinity 100 ppm, aiming for 7.5. That is a drop of 0.4, so 4 × 5 fl oz × 2 = about 40 fluid ounces of muriatic acid — a little over a quart. Add half, run the pump for four hours, re-test, then decide on the rest.
Assumptions
- Doses are calculated from the product strength you selected, not a generic chart.
- Pool volume is accurate — a volume that is out by a quarter puts every dose out by a quarter.
- Water is circulating while the chemical is added and for several hours afterwards.
- Soda ash (sodium carbonate) is the pH increaser. Borax behaves differently and is not what this dose is based on.
Limitations
- Test kits vary. Strips are convenient but a drop-based kit is markedly more reliable for anything beyond a rough check.
- Products degrade. Liquid chlorine loses strength within weeks of manufacture, especially in heat, so an older jug delivers less than its label claims.
- These figures are estimates for a typical residential pool, not a prescription for your specific water.
- pH dosing is inherently approximate. Aeration, rainfall, salt cells and fresh fill water all push pH around between tests.
- Acid lowers alkalinity as well as pH; soda ash raises both. Expect to re-check alkalinity after any pH adjustment.
Questions people ask
Why does my pool pH keep rising?
Aeration. Waterfalls, fountains, spa jets and salt chlorinators all drive carbon dioxide out of the water, which lifts pH. High alkalinity makes it worse. Bringing TA down toward 80 ppm usually slows the climb.
What happens if pH is too low?
Acidic water corrodes metal fittings, heater cores and pump seals, etches plaster, and stings eyes. Below 7.0 the damage is quick enough to be expensive, so low pH is more urgent than high.
Can I use baking soda to raise pH?
Only a little. Baking soda mainly raises alkalinity and lifts pH slightly as a side effect. To move pH specifically, soda ash is the right product — and this calculator is based on it.
How long before I re-test?
Four hours of circulation, minimum. Testing sooner reads whatever is near the sample point rather than the pool.