Water chemistry

How to Raise Pool Alkalinity With Baking Soda

Baking soda dose chart by pool size, a worked trichlor plaster pool example and when to use soda ash instead for low pH.

Sodium bicarbonate, sold as baking soda or as an alkalinity increaser, is the standard way to raise total alkalinity (TA). The dose is about 1.4 lb per 10 ppm per 10,000 gallons. If you buy a branded alkalinity increaser, confirm on the label that it is sodium bicarbonate.

Baking soda dose chart

Pounds of sodium bicarbonate, approximate:

If the volume is a guess, every number above is off by the same percentage. Measure the pool first.

Baking soda or soda ash

Both raise TA. They differ in how much they push pH.

The mistake to avoid is dosing soda ash for a TA problem. pH jumps, then slides back, and TA stays low.

Worked example: 16,000 gallon plaster pool using trichlor

Readings: TA 60, pH 7.4. The pool runs a trichlor feeder, so you want TA in the 80 to 120 range that is common for plaster pools with trichlor. Target 90 ppm.

Raise needed: 90 - 60 = 30 ppm. The multiplier is 16,000 / 10,000 = 1.6.

1.4 lb x 3 x 1.6 = about 6.7 lb of sodium bicarbonate.

1. Weigh out about 3.4 lb, which is half.
2. With the pump running, broadcast it across the deep end of the pool. Do not dump it in one pile or in the skimmer.
3. Brush any that settles on the floor.
4. Let the water circulate, then retest TA and pH.
5. Add the rest if TA has not reached 90.

Splitting the dose lets you catch an overshoot. Water can look cloudy for a short while after a large dose. That usually clears with circulation.

Why trichlor pools run low

Trichlor is acidic. Every feeder cycle pulls pH and TA down a little. A plaster pool on trichlor often needs TA topped up, and that is one reason the 80 to 120 range is common for those accounts. Trichlor also adds about 6 ppm CYA for every 10 ppm FC it adds, so keep an eye on CYA while you are fixing TA.

Account for CYA in your TA reading

Cyanuric acid counts toward the TA reading on a standard test. Many techs use carbonate alkalinity, which is TA minus about one third of CYA, when they judge scale or etching risk.

Example: TA 100 with CYA 60 gives about 80 ppm of carbonate alkalinity (100 - 60 / 3). The test says 100, and the water behaves more like 80. This matters most on pools with high CYA, such as salt pools running 60 to 80 ppm. The saturation index explained shows where that number goes.

Steps for any TA raise

1. Test TA, pH and CYA. Write them down.
2. Pick a target in range. For most pools that is 80 to 100 ppm.
3. Work out the raise and multiply by gallons divided by 10,000.
4. Dose half to two thirds, circulate, retest.
5. Finish with a small second dose if needed.
6. Retest pH last. If it rose above range, bring it down with a small acid dose. The lower pH guide has the chart.

Mistakes

• Skipping the retest. Cloudiness right after dosing is normal, so wait before judging.
• Raising TA higher than needed. High TA pushes pH up and invites scale.
• Reading the target off one test on one day. Test again at the next visit, because TA slides on trichlor pools.
• Mixing baking soda with other chemicals in a bucket. Add each product to the pool separately.

Safety

Follow the product label and SDS. Never mix chemicals. Add chemical to water, never water to chemical. Wear gloves and a dust mask when you are scooping powder on a windy day.

If the same account needs TA every week, look at the feeder and the sanitizer. Chlorine types compared shows what each product does to pH and alkalinity, and the pH and alkalinity dose tool handles the math for any pool size.