How to raise alkalinity in a pool

Total alkalinity is the number people skip, and it's often the reason pH won't behave. If your pH swings every time you add something, low alkalinity is the first thing to check.

What alkalinity does

The Pool & Hot Tub Alliance defines total alkalinity as the water's "pH buffering capacity." Think of it as a shock absorber for pH. With enough of it, rain, swimmers and chemicals barely move your pH. Without it, the Pool & Hot Tub Alliance warns, pH "may quickly drift out of the proper range."

Multnomah County's pool fact sheet calls this "pH bounce." Low alkalinity can also lead to corrosion and metal staining, partly because it lets pH fall, and Shasta County and San Francisco both tie low pH to corroded metal and etched plaster.

What the number should be

CDC's pool code allows 60 to 180 ppm. The Pool & Hot Tub Alliance's ideal depends on your chlorine. With liquid chlorine, cal-hypo or a salt cell, it's 80 to 100 ppm. With dichlor or trichlor, it's 100 to 120 ppm.

If you're below 80, raise it.

Baking soda raises alkalinity

Use sodium bicarbonate, the same stuff as kitchen baking soda. Orenda and Pool & Spa News both point out that it raises alkalinity with only a small effect on pH, which makes it easy to work with.

The amount is well established. Indiana's health department and Wojtowicz's published formula both put it at about 1.4 lb of baking soda per 10 ppm per 10,000 gallons. (The Pool & Hot Tub Alliance rounds up to 1.5 lb.)

Pool size	Raise 10 ppm	Raise 20 ppm	Raise 30 ppm
10,000 gal	22 oz	2 lb 13 oz	4 lb 3 oz
15,000 gal	2 lb 2 oz	4 lb 3 oz	6 lb 5 oz
20,000 gal	2 lb 13 oz	5 lb 10 oz	8 lb 6 oz
25,000 gal	3 lb 8 oz	7 lb	10 lb 8 oz

For your exact numbers, use the alkalinity calculator.

How to add it

1. Test alkalinity and pH, and write both down.
2. Work out the full amount, then plan to add about half now.
3. With the pump running, spread the baking soda over the surface of the pool.
4. Let it circulate for several hours, then retest.
5. Add the rest if you still need it.

None of the sources we checked give a hard maximum per dose. Adding it in stages means you never overshoot.

Baking soda or soda ash?

They're related and easy to mix up. Soda ash (sodium carbonate) is sold as "pH up." Orenda notes that a small dose of it can raise pH substantially. It raises alkalinity too, but it's mainly a pH product. Yakima County's table shows 6 oz of soda ash raising pH 0.2 in 10,000 gallons while adding only about 5 ppm of alkalinity.

So the rule is simple. If alkalinity is low and pH is fine, use baking soda. If both are low, Pool & Spa News suggests soda ash can make sense, since it moves both. If only pH is low, use soda ash and the pH calculator.

Fix alkalinity before pH

The Pool & Hot Tub Alliance says to correct alkalinity before adjusting pH. It makes sense once you know what alkalinity does. If you fix pH first, it'll drift again the moment you change alkalinity.

How often to test it

Alkalinity moves slowly. Hayward and South Australia's health department both suggest testing it about once a week, alongside your daily chlorine and pH checks. The weekly test log has a column for it.