How to Lower or Raise pH in a Pool
pH is the pool number you will adjust most often. Too high and chlorine works slowly, scale forms and the water can cloud; too low and the water stings eyes, etches plaster and corrodes metal. The fix is simple once you know one thing: how much a dose moves pH depends on your total alkalinity, not just on your pool volume.
The target
Keep pH between 7.2 and 7.8, ideally 7.4 to 7.6. That range matches the CDC Model Aquatic Health Code and is comfortable for swimmers. Chlorine is more active at the lower end, scale is less likely, and eyes are happiest around 7.4–7.6.
Why alkalinity changes the dose
Total alkalinity (TA) is mostly dissolved bicarbonate, which soaks up acid and base. A pool with TA at 120 ppm can take roughly twice as much acid as a pool at 60 ppm for the same pH change. That is why “add a cup of acid per 10,000 gallons” rules are so unreliable.
| Total alkalinity | Lower 7.8 → 7.5 (31.45% muriatic) | Raise 7.2 → 7.5 (soda ash) |
|---|---|---|
| 60 ppm | 6.96 fl oz | 13.3 oz |
| 80 ppm | 8.72 fl oz | 1.05 lb |
| 100 ppm | 10.5 fl oz | 1.27 lb |
| 120 ppm | 12.2 fl oz | 1.49 lb |
Per 10,000 gallons with CYA at 30 ppm, computed with the pH calculator's carbonate model. Add about 75% first and retest.
For your exact pool, enter pH, target, TA and CYA in the pool pH calculator. If pH keeps swinging back, adjust TA first with the alkalinity calculator.
How to lower pH
Muriatic acid (hydrochloric acid, usually 31.45% or a “low-fume” 14.5%) is the most common and cheapest option. Dry acid (sodium bisulfate) is a granular alternative that is easier to store and handle but adds sulfates over time.
- Test pH and total alkalinity.
- Calculate the dose and add about three-quarters of it first.
- With the pump running, pour the acid slowly into the deep end or in front of a return jet. Pre-dissolve dry acid in a bucket of pool water.
- Wait at least 30 minutes for it to circulate, then retest and add the rest if needed.
Safety: always add acid to water, never water to acid. Wear gloves and eye protection, stand upwind of the fumes, and never let acid come into contact with chlorine products; the two together release chlorine gas.
How to raise pH
There are two ways, and the right one depends on alkalinity.
- Aeration raises pH without changing total alkalinity. Point return jets up at the surface, run waterfalls, fountains or spa spillovers, or add an air pump. It is slow but free, and ideal when TA is already in range.
- Soda ash (sodium carbonate) raises pH quickly and also raises TA. Use it when both pH and alkalinity are low. Pre-dissolve it in a bucket and add it slowly; adding too much at once can cloud the water temporarily.
- Borax raises pH with less effect on TA than soda ash, a middle ground some owners prefer.
- Baking soda is mainly for alkalinity; it nudges pH up only slightly.
Why does pH keep rising?
Pool water naturally loses dissolved carbon dioxide to the air, and as CO₂ leaves, pH goes up. Anything that speeds that up raises pH faster:
- High total alkalinity, the most common cause. Lowering TA to 60–80 ppm often fixes it.
- Salt chlorine generators, which push pH up as they make chlorine.
- Water features and aeration, which drive off CO₂.
- New plaster, which releases alkaline material for the first months.
Why does pH keep dropping?
Less common, but it happens with trichlor tablets (which are acidic), heavy rain in areas with acidic rainwater, and very low alkalinity that leaves no buffer.
pH and the bigger picture
pH also controls whether your water is balanced overall. Combined with calcium, alkalinity and temperature, it determines the Langelier Saturation Index. If you are fighting scale or etching, check the LSI calculator: sometimes the right fix is a small pH change rather than more calcium or less alkalinity.