How to raise pH and alkalinity in a pool
Low pH and low alkalinity usually show up together, and the fix depends on which one is actually low. Test both first. Then pick the product that moves the number you need, and leave the other one alone.
Start with two readings
- pH: the CDC recommends 7.0–7.8 for pools. Many owners aim for about 7.4–7.6.
- Total alkalinity (TA): the water's buffer, which holds pH steady. Common targets are 60–120 ppm, with the lower half of that range often suiting saltwater pools and pools that use liquid chlorine.
Also note your stabilizer (CYA) reading. Cyanuric acid adds a little to the alkalinity reading, and the calculators below account for it.
Which product to use
| Your readings | Use | What it does |
|---|---|---|
| pH low, TA in range or high | Aeration | Raises pH and leaves TA unchanged. No chemical added. |
| pH low, TA low | Soda ash (sodium carbonate, "pH up") | Raises pH strongly and TA moderately. |
| pH in range, TA low | Baking soda (sodium bicarbonate, "alkalinity up") | Raises TA with only a small rise in pH. |
| pH low, TA in range, want extra buffering | Borax | Raises pH with a smaller effect on TA, and adds borate, which helps resist pH swings. |
The most common mistake is using soda ash when only pH is low. It pushes alkalinity up too, and high alkalinity makes pH drift upward later, so you end up adding acid to undo it.
Why pH and alkalinity drop
- Trichlor tablets and dichlor. Both are acidic and slowly pull pH and alkalinity down. This is the most common cause in pools that use a floater or tablet feeder.
- Too much acid. A full calculated acid dose added at once, or acid added to lower alkalinity without aerating in between.
- Rain and fill water. Rain is usually slightly acidic and has almost no alkalinity, so heavy rain dilutes TA. Some fill water is also low in alkalinity.
- Low alkalinity to begin with. With little buffer, small additions swing pH a lot.
How to raise pH
If alkalinity is fine: aerate
Pool water holds dissolved carbon dioxide. Driving it out raises pH without changing alkalinity. Point return jets up so they break the surface, run waterfalls, fountains or a spa spillover, and leave the cover off. pH typically climbs over a day or two. Retest before adding anything.
If alkalinity is low too: soda ash
- Work out the dose with the pH calculator. Enter your alkalinity and CYA: the dose depends heavily on them.
- Pre-dissolve the soda ash in a bucket of pool water (add the product to the water, not the water to the product).
- With the pump running, pour it slowly around the deep end or in front of a return jet.
- Add about three-quarters of the dose, circulate for at least an hour, retest, then add the rest if needed.
Soda ash can turn the water briefly cloudy, especially in hard water or when added fast. That normally filters out. Follow the label of the product you buy.
How to raise total alkalinity
- Work out the amount with the alkalinity calculator. In 10,000 gallons, about 1.4 lb of baking soda raises TA by 10 ppm.
- Broadcast the baking soda over the surface of the deep end with the pump running. It dissolves easily.
- Add no more than about half the total at once, wait a few hours, retest, then continue.
- Check pH afterwards. Baking soda nudges it up a little, and aeration can finish the job if needed.
Worked example
A 15,000-gallon pool reads pH 7.0, alkalinity 50 ppm and stabilizer 30 ppm. The owner uses trichlor tablets, which explains both low readings.
- Raise pH to 7.4 with soda ash: the pH calculator gives about 1.78 lb of soda ash. Afterwards, alkalinity is about 63 ppm.
- Then raise alkalinity: to bring 63 ppm up to 90 ppm in the same pool, the alkalinity calculator gives about 5.67 lb of baking soda. Split it into two or three additions, and recheck pH at the end.
Compare a pool with the same pH and stabilizer but alkalinity of 100 ppm: the pH calculator gives about 3.17 lb of soda ash for the same 7.0 to 7.4 move, and alkalinity ends near 124 ppm. That pool would do better with aeration alone.
Because the tablets keep pulling pH down, this owner will be adding base regularly. Switching some of the chlorine to liquid chlorine, or keeping alkalinity near the top of the range, slows the drop.
Common mistakes
- Adding the full dose at once. Test kits read pH in steps of 0.1–0.2. Add part, circulate, retest.
- Testing pH right after shocking. Very high chlorine can make common pH reagents read falsely high, which hides a low pH. Retest once chlorine is back in its normal range.
- Raising pH with soda ash when only alkalinity is low. Use baking soda for alkalinity.
- Ignoring calcium. Raising pH and alkalinity in hard water can push the water toward scaling. Check the LSI after big changes.
- Mixing products. Add one chemical at a time, and never mix pool chemicals together. See pool chemical safety.
Frequently asked questions
Is baking soda the same as soda ash?
No. Baking soda is sodium bicarbonate and mainly raises alkalinity. Soda ash is sodium carbonate and raises pH much more strongly. Plain baking soda from the grocery store works the same as "alkalinity increaser" if the box lists only sodium bicarbonate.
What happens if pH is too low?
The water can sting eyes, etch plaster and grout, corrode metal parts such as heater exchangers and ladders, and wrinkle vinyl liners over time.
Can I swim after adding soda ash or baking soda?
Follow the product label. A common approach is to wait until the product has dissolved and circulated, and to retest before swimming.
Why does my pH keep dropping?
Most often it's acidic chlorine (trichlor or dichlor) combined with low alkalinity. Raise alkalinity into range so pH has a buffer, and consider an unstabilized chlorine source for part of the time.