Pool chemical for alkalinity: baking soda and acid dosing
Sodium bicarbonate, plain baking soda, raises total alkalinity at a rate of about 1.5 pounds per 10,000 gallons for every 10 ppm you need to add. Muriatic acid lowers it at roughly 1 quart (32 fl oz) of standard 31.45% acid per 10,000 gallons per 10 ppm removed. Both numbers scale directly with pool size, and both should be staged rather than dumped in all at once.
Total alkalinity is the buffer that keeps pH from swinging after every chemical addition, rain event, or top-off. The target band is 80 to 120 ppm; below that, pH bounces around unpredictably, and above it, pH tends to creep upward on its own and drags scale-forming conditions with it.
How much baking soda do you need to raise alkalinity?
Use this formula: (pool gallons ÷ 10,000) × (ppm increase needed ÷ 10) × 1.5 lb = pounds of baking soda.
Worked example: a 15,000-gallon pool testing 70 ppm alkalinity, needing to reach 100 ppm (a 30 ppm rise), needs (15,000 ÷ 10,000) × (30 ÷ 10) × 1.5 = 1.5 × 3 × 1.5 = 6.75 pounds of baking soda, roughly 7 pounds.
Don’t add more than about 1.5 pounds per 10,000 gallons in a single dose, even if the math calls for more. For the 7-pound example above, that means adding it in one dose is fine for this size increase, but a bigger jump, say from 40 ppm to 100 ppm, would need staging across two applications six hours apart rather than one large dump, since a single oversized dose can spike pH and cloud the water before it fully dissolves.
How much muriatic acid do you need to lower alkalinity?
Use this formula: (pool gallons ÷ 10,000) × (ppm decrease needed ÷ 10) × 32 fl oz = ounces of 31.45% muriatic acid.
Worked example: the same 15,000-gallon pool now testing 150 ppm alkalinity, needing to drop to 100 ppm (a 50 ppm decrease), would calculate to (15,000 ÷ 10,000) × (50 ÷ 10) × 32 = 1.5 × 5 × 32 = 240 fl oz, about 1.9 gallons of acid. That’s too much for one treatment.
Cap any single acid treatment at a 10 to 20 ppm drop. For a 50 ppm total decrease, split it into three doses spaced 24 hours apart: roughly 96 fl oz (3 quarts) for the first 20 ppm drop, another 96 fl oz for the second 20 ppm, and 48 fl oz for the final 10 ppm, retesting before each addition since acid concentration and water temperature both shift the actual result slightly from the formula.
Alkalinity dosing at a glance (per 10,000 gallons, per 10 ppm)
| Direction | Chemical | Amount per 10,000 gal per 10 ppm | Max per single dose |
|---|---|---|---|
| Raise | Sodium bicarbonate (baking soda) | 1.5 lb | 1.5 lb per 10,000 gal |
| Lower | Muriatic acid (31.45%) | 32 fl oz (1 quart) | 20 ppm drop, then wait 24 hours |
Why does acid concentration change the math?
Retail muriatic acid is most commonly sold at 31.45% strength in the US, but some brands and regions sell 20% or other concentrations, and the dose has to scale with it. Always check the product label’s percentage before using a generic dosing chart; a 20% acid needs roughly 50% more volume than 31.45% acid to hit the same ppm drop. This is the exact reason different pool-chemistry sources quote different ounce figures for the “same” 10 ppm drop: they’re often quoting different acid strengths without saying so.
Why not just use soda ash to fix low alkalinity?
Soda ash (sodium carbonate) raises both pH and alkalinity at once, roughly 0.2 pH units and 5 ppm alkalinity per 6 ounces per 10,000 gallons, which makes it a poor tool when alkalinity is low but pH is already fine. Baking soda raises alkalinity with only a mild pH effect, which is why it’s the standard choice for an alkalinity-only correction. Reach for soda ash when both pH and alkalinity are low together, and baking soda when alkalinity alone needs the lift.
Pouring technique matters for the acid side specifically: always add acid to water, in a wide arc across the deep end with the pump running, never water to acid, and never in one concentrated spot near a liner or steps.
Skip the manual math and run your exact gallon count, current reading, and target through the ClearCove Pools pool chemical calculator; it stages the doses automatically so you’re not eyeballing a 24-hour wait between acid treatments.
If alkalinity is off because the pool just came out of winter, the ClearCove Pools pool-opening guide has the full spring sequence, which puts alkalinity first for exactly this reason.
Frequently asked questions
Can I use washing soda instead of baking soda for alkalinity? No. Washing soda is sodium carbonate, chemically the same as soda ash, and it raises pH much more aggressively than plain baking soda (sodium bicarbonate). Using it in place of baking soda will overshoot pH.
How often should I test alkalinity? Weekly during the swim season, and after any heavy rain, top-off, or chemical correction, since alkalinity shifts less often than chlorine but drifts silently until pH starts swinging.
Why did my alkalinity go up after I only added chlorine? Some chlorine products, particularly cal-hypo and dichlor, carry a mild alkalinity or pH side effect depending on the base compound. Check the product label; if alkalinity keeps climbing on a pool using only liquid chlorine, the source is more likely fill water or a leak pulling in groundwater.
Is high alkalinity dangerous? Not directly to swimmers, but alkalinity above 120 to 150 ppm makes pH resistant to correction and tends to push the water toward cloudiness and scale formation over time.
Bottom line: 1.5 pounds of baking soda per 10,000 gallons raises alkalinity 10 ppm, and 1 quart of 31.45% muriatic acid per 10,000 gallons lowers it 10 ppm. Stage anything bigger than a 20 ppm move across multiple treatments and retest before each one.