How to Raise Alkalinity in a Pool

To raise alkalinity in a pool, add sodium bicarbonate — ordinary baking soda. For every 1.5 pounds you add per 10,000 gallons of water, total alkalinity rises by approximately 10 ppm. If your alkalinity has dropped below 80 ppm, your pH is almost certainly unstable, and no amount of pH adjuster will fix that until you restore the buffer.

Alkalinity is the parameter I ignored longest when I started maintaining my own pool. I spent a full season chasing pH — adding acid one week, soda ash the next — and it never held. The problem was not pH. It was that my alkalinity had drifted down to 50 ppm, and at that level, pH has nothing anchoring it in place.

What Alkalinity Actually Does

Total alkalinity measures how well your water resists changes in pH. It is a chemical buffer — a shock absorber that keeps pH from lurching every time you add chlorine, a rainstorm hits, or a group of swimmers jumps in.

Here is what that means in practice. In a pool with alkalinity at 100 ppm, adding a cup of muriatic acid might lower pH from 7.6 to 7.4 — a small, controlled shift. In a pool with alkalinity at 40 ppm, that same cup of acid could drop pH from 7.6 down to 6.8. Same pool volume, same acid, same dose. The only difference is whether the buffer is there to absorb the change.

The chemistry is straightforward. Alkalinity in pool water comes primarily from bicarbonate ions (HCO₃⁻). These ions react with both acids and bases, neutralizing them before they shift pH. When alkalinity is low, there are not enough bicarbonate ions to absorb those additions, so pH moves fast and far in response to small inputs.

If your pH refuses to stay where you set it despite repeated adjustments, test your alkalinity. Low alkalinity is the most likely cause. Fix the buffer first. The pH will follow.

What Your Alkalinity Should Be

For residential pools, total alkalinity should be between 80 and 120 ppm. This range provides enough buffering capacity to keep pH stable between routine maintenance sessions and is consistent with guidelines from the Pool & Hot Tub Alliance (PHTA).

Below 80 ppm, pH becomes increasingly volatile. Above 120 ppm, pH tends to creep upward and resist correction — and you may start seeing cloudy water or calcium scale forming on tile lines and equipment.

If your pool has a vinyl liner or fiberglass shell, aim for the lower half of the range (80–100 ppm), where scaling risk is lower. Plaster and concrete pools handle 100–120 ppm without issue.

Why Alkalinity Drops

Alkalinity does not drop for mysterious reasons. Four things cause it:

Acid additions. Every time you add muriatic acid or sodium bisulfate to lower pH, you also lower alkalinity. This is the single most common cause of gradually declining alkalinity. If you add acid regularly, alkalinity is falling as a side effect — test it.

Rain. Rainwater has near-zero alkalinity and a slightly acidic pH, around 5.0 to 5.5 for typical rainfall. Heavy or prolonged rain both dilutes your existing alkalinity and introduces acid into the pool. Test alkalinity after any significant storm if your pool is uncovered.

Fill water. Tap water alkalinity varies widely by region — from under 30 ppm in soft-water areas to above 200 ppm in hard-water areas. If your source water has low alkalinity, every top-off dilutes your pool's buffer. Test your fill water once so you know what you are working with.

Bather load and organic debris. Swimmers introduce organic acids — sweat, sunscreen, body oils. Leaves and other debris decompose and produce acids as they break down. In a heavily used pool with borderline alkalinity, these inputs push the buffer below the threshold where pH becomes unstable.

How to Raise Alkalinity with Baking Soda

Sodium bicarbonate is the only chemical you need. Pool stores sell it labeled as "alkalinity increaser" or "alkalinity up" at a premium. Grocery store baking soda is the same compound — NaHCO₃. The chemistry is identical. The only difference is the price.

Dosage Table: Sodium Bicarbonate

All amounts are per 10,000 gallons of pool water. Test your current alkalinity before calculating.

TA Increase Needed	Baking Soda to Add	Additions (1.5 lbs max each)	Total Wait Time
10 ppm	1.5 lbs	1	6 hours
20 ppm	3.0 lbs	2	12 hours
30 ppm	4.5 lbs	3	18 hours
40 ppm	6.0 lbs	4	24 hours

For different pool sizes, scale proportionally. A 15,000-gallon pool needs 2.25 lbs per addition for a 10 ppm increase. A 20,000-gallon pool needs 3.0 lbs per addition. If your pool volume is somewhere in between or you would rather not do the math, the pool chemical calculator guide covers how to calculate exact doses for any volume.

Step-by-Step Procedure

1. Test your water. Test your alkalinity and pH with a test kit or test strips. You need both readings because sodium bicarbonate raises pH slightly in addition to raising alkalinity.

2. Calculate the dose. Subtract your current alkalinity from your target. If your reading is 60 ppm and your target is 100 ppm, you need a 40 ppm increase — 6.0 lbs of baking soda per 10,000 gallons, split across four separate additions.

3. Measure no more than 1.5 lbs per 10,000 gallons for a single addition. Adding more at once can spike pH and create localized high-alkalinity zones near the pour site. Smaller additions mix more evenly.

4. Pre-dissolve the baking soda. Fill a clean 5-gallon bucket about three-quarters full with pool water. Pour the measured baking soda into the bucket and stir until dissolved. This prevents undissolved powder from settling on the pool floor.

5. Pour with the pump running. Walk the dissolved solution around the perimeter of the pool, pouring slowly. Stay away from the skimmer so the concentrated solution circulates through the full volume.

6. Wait at least 6 hours. Let the pump circulate the water fully before retesting. If alkalinity is still below target, repeat with another 1.5 lb addition. Do not rush this — each addition needs time to distribute.

7. Adjust pH after alkalinity is in range. Baking soda typically raises pH by 0.1 to 0.3 per addition. Once your alkalinity reads 80–120 ppm, check pH. If it has drifted above 7.6, a small dose of muriatic acid will bring it back down. The Pool app's dosage calculator handles both adjustments — enter your current readings and pool volume, and it returns exact amounts for alkalinity and pH correction, including how to split additions safely.

What If Alkalinity Is Too High

Alkalinity above 120 ppm pushes pH upward and makes it resist correction. Cloudy water and white calcium scale on the waterline, tile, and fittings are common visible signs. If you are adding acid to lower pH and it keeps bouncing back up within a day or two, high alkalinity is likely the reason.

To lower alkalinity, use muriatic acid (hydrochloric acid, typically sold at 31.45% concentration) or sodium bisulfate (dry acid). Both lower alkalinity and pH at the same time.

Acid Dosage to Lower Alkalinity

Per 10,000 gallons. Test your alkalinity and pH before adding acid. Add acid in increments — test after 4 hours before adding more.

TA Decrease Needed	31.45% Muriatic Acid	Sodium Bisulfate (dry acid)
10 ppm	26 fl oz	2.0 lbs
20 ppm	52 fl oz	4.0 lbs
30 ppm	78 fl oz	6.0 lbs

If your muriatic acid is a diluted formulation (14.5% or 20% are common at hardware stores), you will need proportionally more. Check the label for concentration. [VERIFY: dry acid dosages are calculated from anhydrous sodium bisulfate — product purity varies by brand. Check the product label for recommended doses and adjust.]

The Aeration Technique: Lowering Alkalinity Without Crashing pH

Acid lowers pH and alkalinity simultaneously. If you need alkalinity to come down but your pH is already at or below 7.4, a straight acid dose will push pH into corrosive territory.

The fix is aeration. After adding acid, you can raise pH back up without raising alkalinity by increasing surface agitation:

• Point one or more return jets upward so they break the water surface
• Run a waterfall, fountain, or spa jets
• Angle a garden hose to splash across the pool surface if you have no built-in features

Aeration drives dissolved CO₂ out of the water. Losing CO₂ shifts the carbonate equilibrium and raises pH — but it does not add bicarbonate ions, so alkalinity stays where the acid put it.

The cycle:

1. Add acid → both pH and alkalinity drop
2. Aerate for 12–24 hours → pH rises back to 7.4–7.6, alkalinity stays low
3. Test both values
4. If alkalinity is still above target, repeat from step 1

Each cycle typically lowers alkalinity by 10–15 ppm while returning pH to its starting point. For a pool at 180 ppm targeting 100 ppm, plan on five or six cycles spread over three to four days. It is not fast, but it works without damaging surfaces or equipment the way sustained low pH would.

When pH and Alkalinity Are Both Off

This is the scenario that confuses pool owners most: alkalinity reads low while pH is high, or alkalinity is high while pH is low. Since acid and base both affect both values, it can feel like fixing one breaks the other.

It does not have to. Here is how to approach each combination:

Low alkalinity + low pH. The straightforward case. Add baking soda. It raises both values. This is the most common situation after heavy rain or a string of acid additions.

Low alkalinity + high pH. Fix alkalinity first. Add baking soda to bring total alkalinity into the 80–120 ppm range, even though it temporarily pushes pH higher. Once the buffer is restored, lower pH with a small acid dose. With proper alkalinity in place, the pH correction will hold instead of bouncing back within a day. CYA also plays a buffering role in your water chemistry — if your cyanuric acid is below 30 ppm in an outdoor pool, that compounds the pH instability.

High alkalinity + low pH. Add muriatic acid in small increments — 8 to 10 fl oz per 10,000 gallons at a time. Acid lowers both values, which is what you want, but go slowly and test after 4 hours to avoid overshooting pH downward. If pH drops below 7.2 between additions, aerate before adding more acid.

High alkalinity + high pH. Add muriatic acid. Both parameters need to come down, and acid pushes both in the right direction. This is the easiest combination to correct. Add acid, wait 4 hours, test, and repeat until both values are in range.

Frequently Asked Questions

How much baking soda do I need to raise pool alkalinity?

Add 1.5 pounds of sodium bicarbonate per 10,000 gallons of pool water to raise total alkalinity by approximately 10 ppm. Test your current alkalinity, calculate the gap to your target of 80–120 ppm, and add no more than 1.5 pounds per 10,000 gallons per addition. Wait at least 6 hours between additions and retest before adding more.

Can I use regular baking soda instead of pool alkalinity increaser?

Yes. Grocery store baking soda is sodium bicarbonate — the same chemical compound sold under pool brand labels at a higher price. There is no difference in how the two products affect your water. If you only adjust alkalinity a few times per season, a few boxes of baking soda and the dosage table above are all you need.

Why does my pool alkalinity keep dropping?

Repeated acid additions are the most common cause. Every dose of muriatic acid or dry acid lowers pH and alkalinity together. Heavy rain dilutes alkalinity and adds weak acid (rain pH is around 5.0–5.5). Topping off with low-alkalinity tap water dilutes the buffer further. If your alkalinity drops faster than you expect, check whether frequent pH corrections are pulling it down as a side effect.

What happens if pool alkalinity is too low?

Below 80 ppm, your pool loses its pH buffer. A single rainstorm or a small acid addition can swing pH from 6.8 to 8.2 within hours. These rapid swings irritate eyes and skin, corrode metal equipment (heaters, ladders, pump seals), etch plaster surfaces, and make it nearly impossible to hold chlorine at a stable level.

How do I lower pool alkalinity without lowering pH?

Add muriatic acid to lower both values, then aerate the water (point return jets upward, run a waterfall or spa jets, or splash the surface) to raise pH back up without affecting alkalinity. Aeration drives off dissolved CO₂, which raises pH while alkalinity stays where the acid set it. Repeat this acid-then-aerate cycle — each round lowers alkalinity by about 10–15 ppm — until you reach your target range of 80–120 ppm.