PooloraHow to raise pH in a pool
Low pH stings eyes and slowly eats plaster, grout and metal. Before raising it, check alkalinity: it decides which product to use.
- Below pH 7.2, raise it; never let it sit below 7.0.
- If alkalinity is low, raise it with baking soda first. If alkalinity is fine, use soda ash or aeration.
- In 10,000 gallons with alkalinity 80, pH 7.2 → 7.5 takes about 1 lb (16 oz · 465 g) of soda ash.
When to raise pH
The industry range is 7.2–7.8 (ANSI/APSP/ICC-11) and the CDC accepts 7.0–7.8. Below that, water becomes aggressive: it stings eyes, etches plaster and corrodes heaters, ladders and pump parts.
Step 1: look at alkalinity first
Low pH often comes with low total alkalinity (TA), for example after weeks of acid or tablets. If TA is below your range (80–100 ppm with liquid chlorine or salt, 100–120 with tablets), raise it with baking soda first: it adds buffer and nudges pH up a little. Per 10,000 gallons:
| Raise TA by | Baking soda |
|---|---|
| 10 ppm | 1.4 lb 635 g |
| 20 ppm | 2.8 lb 1.25 kg |
| 30 ppm | 4.2 lb 1.9 kg |
Retest pH after the baking soda has circulated: if it is now 7.2 or higher, you are done, with no soda ash at all.
Step 2: soda ash if alkalinity is fine
Soda ash (sodium carbonate) raises pH strongly and alkalinity too. Amounts for 10,000 gallons (water at 80 °F, calcium 300, stabilizer 40):
| Total alkalinity | pH 7.0 → 7.5 | pH 7.2 → 7.5 |
|---|---|---|
| 60 ppm | 1.7 lb 775 g | 13 oz 375 g |
| 80 ppm | 2.1 lb 970 g | 1 lb 465 g |
| 100 ppm | 2.6 lb 1.15 kg | 1.2 lb 560 g |
For other sizes, scale by volume or use the pool chemical charts by size. Pre-dissolve soda ash in a bucket of pool water and pour it slowly with the pump running; adding a lot at once can cloud the water for a while.
Step 3: or use air, for free
Aeration raises pH without adding alkalinity, because it lets dissolved carbon dioxide escape. Point return jets up to break the surface, run waterfalls or fountains, and let it work for a day. It is slow, but it is the right tool when alkalinity is already where you want it.
Why pH drops
- Trichlor tablets are acidic: they pull pH and alkalinity down week after week.
- Too much acid in a previous correction.
- Rain, which is often slightly acidic and also dilutes alkalinity.
- Low alkalinity, which lets pH swing with every small change.
If the cause is tablets, plan on raising alkalinity regularly or switching to liquid chlorine.
Do not overshoot
Add about half of the calculated dose, let it circulate and retest. Raising pH too far just means buying acid to bring it back. And keep chlorine for the end: once pH is right, chlorine works better.
Common questions
Is baking soda the same as soda ash?
No. Baking soda (sodium bicarbonate) mostly raises alkalinity. Soda ash (sodium carbonate) mostly raises pH. Many "pH up" products are soda ash; many "alkalinity up" products are baking soda.
Why does my pH keep dropping?
Trichlor tablets are acidic, and rain is often slightly acidic too. If you use tablets, expect to raise pH and alkalinity regularly.
Do it with your own products
Poolora turns your test into the exact amount of the products on your shelf, in cups and ounces, in the right order, and tells you when it's safe to swim. Free to start; every chemical, water balance and history are part of Pro.
Keep going
Sources
- ANSI/APSP/ICC-11 (pH 7.2–7.8)
- CDC: Home pool and hot tub water treatment and testing (pH 7.0–7.8)
- Pool & Hot Tub Alliance (PHTA): alkalinity fact sheet
- Doses: Poolora engine (mass balance for chlorine; carbonate-equilibrium model for pH with constants from the USGS PHREEQC database)