Pool Alkalinity Calculator

What total alkalinity does

Total alkalinity (TA) measures the bicarbonate and carbonate in the water, reported in ppm as calcium carbonate. It acts as a buffer for pH: with enough alkalinity, pH stays steady; with too little, every splash of chlorine or acid makes pH swing; with too much, pH keeps drifting upward and is hard to bring down, and scale forms more easily.

Australian Standard AS 3633, quoted by the pool industry body SPASA, gives a total alkalinity range of 60 to 200 ppm, with about 100–120 ppm as a practical target. Many US pool equipment makers suggest roughly 80–120 ppm for plaster pools and somewhat higher for vinyl and fibreglass. Salt pools and pools using trichlor often run better at the lower end, because those systems push pH in opposite directions. Pick a target from your pool builder or equipment maker, then use this calculator to reach it.

Baking soda (g) = ppm increase × litres ÷ 1,000 × 1.68
Muriatic acid 31.45% (mL) = ppm decrease × litres ÷ 1,000 × 0.729 ÷ (0.3145 × 1.16)
Rule of thumb: 1.4 lb baking soda raises 10,000 gal by 10 ppm; 25.6 fl oz of 31.45% acid lowers it by 10 ppm

Worked examples

• Raising TA, 15,000 gallons, 70 → 100 ppm: 6.3 lb (2.86 kg) of baking soda.
• Raising TA, 50,000 litres, 60 → 100 ppm: 3.36 kg (7.4 lb) of baking soda.
• Lowering TA, 15,000 gallons, 160 → 120 ppm: about 1.2 gallons (4.5 L) of 31.45% muriatic acid in total, or 12.9 lb (5.85 kg) of dry acid, added in stages.
• Lowering TA, 50,000 litres, 150 → 120 ppm: about 3 L of 31.45% acid or 7 L of half-strength 14.5% acid, in stages.

Raising alkalinity

1. Use plain sodium bicarbonate (baking soda or "alkalinity increaser"; check the label, they are usually the same chemical).
2. With the pump running, broadcast it across the surface or pre-dissolve it in a bucket.
3. Add no more than about half the dose at a time if it is large, wait 6 hours, and retest.

Baking soda raises pH only a little. If both pH and alkalinity are low, soda ash (sodium carbonate) raises pH more strongly, but it is easy to overshoot, so most owners correct alkalinity first and then pH.

Lowering alkalinity: acid plus aeration

Acid lowers alkalinity and pH together. Pouring the full calculated amount at once would drop pH far too low and could damage surfaces and equipment. The usual method is:

1. Add enough acid to bring pH down to about 7.0–7.2 (do not go lower).
2. Aerate the water: point return jets upward, run waterfalls, fountains or spa jets. This drives off carbon dioxide and raises pH without raising alkalinity.
3. When pH is back near 7.6, repeat. Each cycle lowers alkalinity a bit.

The calculator shows the total acid that the whole alkalinity drop requires, so you know roughly how much to buy and how many cycles to expect.

Acid safety

• Wear gloves and eye protection. Always add acid to water, never water to acid.
• Pour slowly in front of a return jet in the deep end with the pump running, or dilute it in a bucket of pool water first, as the label directs.
• Never mix acid with chlorine. Together they release chlorine gas. Add them hours apart.
• Half-strength (14.5%) muriatic acid is easier to handle and gives off fewer fumes; you just need about twice as much.

Common mistakes

• Chasing pH before alkalinity. If alkalinity is far off, pH will not stay where you put it.
• Forgetting stabilizer. Cyanuric acid adds to the alkalinity test reading. The water balance calculator corrects for it.
• Using a wrong volume. Check it with the pool volume calculator.

Estimates for general information. Always follow the product label and add large doses in stages.

Frequently asked questions

Sources

• SPASA Australia: Water balance (AS 3633 ranges for pH, total alkalinity and calcium hardness).
• CDC: Home pool and hot tub water treatment and testing.
• Doses calculated from molar masses: sodium bicarbonate 84.0 g/mol, hydrogen chloride 36.46 g/mol, sodium bisulfate 120.06 g/mol, calcium carbonate equivalent 50.04 g/mol.

Last reviewed 28 October 2026. Results are estimates; see our disclaimer.