How to Lower or Raise Pool pH: Muriatic Acid, Dry Acid and Soda Ash

Target ranges by source

Sources don’t all publish the same range. Here is what each one says:

The MAHC is written for public pools and doesn’t bind a backyard pool. If you run a salt system, follow its manual first. HTH’s pH Down and pH Up pages both aim for 7.2–7.6.

Why pH matters

CDC says keeping pH in the 7.0–7.8 range “best balances killing germs to prevent swimming-related illness, the lifespan of the pipes, and swimmers’ comfort.” As pH goes up, chlorine kills germs less well, “especially if pH is >8.0.” Below 7.0, chlorine works better but pipes are “more likely to corrode or break down.”

The MAHC annex explains the chemistry. At about pH 7.5, half the free chlorine is hypochlorous acid (HOCl) and half is hypochlorite, and HOCl is “approximately 100 times more effective at killing microorganisms.” Lower pH shifts the balance toward HOCl. The annex also notes that stabilizer (CYA) blunts the effect: without CYA, raising pH from 7.2 to 7.8 cuts HOCl by about 50%, but with 10 ppm CYA or more the cut is about 25%. See the stabilizer guide for more on CYA.

pH also affects surfaces. The annex says low pH “can lead to the water dissolving calcium carbonate from plaster surfaces,” while high pH “can lead to calcium carbonate scaling,” and low pH “can also increase the rate of metal corrosion.”

Check total alkalinity first

Total alkalinity is the water’s buffer. The MAHC annex says it “helps prevent wide variations in pH (pH bounce)”:

• Too low: pH “changes rapidly when chemicals or impurities enter the water.” The annex notes pH can drop fast with net-acidic chlorine such as trichlor tablets and dichlor shock, “causing etching and corrosion.”
• Too high: “pH becomes difficult to adjust,” and high pH often follows, with cloudy water, weaker disinfection, scale and filter problems.
• To raise it: the annex names bicarbonate of soda (sodium bicarbonate, baking soda). HTH Pool Care Alkalinity Up (SKU 67060; a labeled Amazon search), for example, is 100% sodium bicarbonate, and HTH’s page sends you to the product label for the dose.
• To lower it: add acid, which “reacts with bicarbonates in the water and reduces the total alkalinity.”

HTH’s pH Down directions say to “adjust total alkalinity first to help prevent pH drift,” and add that if pH won’t come down after dosing, “high total alkalinity is usually the cause.”

If you use stabilizer, correct the alkalinity reading. Both the MAHC annex and Pentair’s manual say to subtract one-third of the CYA level from the total alkalinity result.

How to lower pH: muriatic acid or dry acid

Muriatic acid and sodium bisulfate (dry acid) both lower pH, and both lower total alkalinity too. HTH’s FAQ puts it plainly: “pH Decreaser (sodium bisulfate or muriatic acid) lowers both pH and total alkalinity.”

Dry acid (sodium bisulfate)

HTH Pool Care pH Down (SKU 67057, 5 lb) is 92% sodium bisulfate. Its directions:

• Turn on the pump and broadcast the dose “evenly over the deepest part of the pool.”
• “Never pre-dissolve pH Down in a plastic bucket.”
• Wait 4–6 hours after a shock treatment before adding it, “to avoid off-gassing.”
• If alkalinity is already in range, use smaller doses and retest often “to avoid dropping alkalinity below 80 ppm.”
• The safety section says to wear goggles and rubber gloves and “do not mix this product with any other chemicals.”

HTH’s dose chart for this product, which applies to HTH pH Down only:

The chart starts at pH 8.0. HTH’s page gives two different waits before retesting, so follow the wait printed on the container.

Salt-system owners, check your manual first. Pentair’s IntelliChlor manual says: “NEVER use dry acid (sodium bisulfate) to adjust pH. A buildup of by-products can damage the SCG.” CircuPool’s manual says the same about its cell. Hayward’s AquaRite manual says dry acid “is discouraged especially in arid regions” where pool water evaporates heavily and is rarely diluted with fresh water. HTH calls its pH Down safe for saltwater pools when used as directed, but on a salt pool, follow the generator maker’s manual.

Muriatic acid

The MAHC lists it as “muriatic (hydrochloric) acid.” Pentair’s manual warns that “working with muriatic acid can be dangerous” and says to wear rubber gloves and eye protection and work in a well-ventilated area. Hayward’s troubleshooting guide warns that “muriatic and other acids can cause severe injury, burns and respiratory problems if not handled properly.”

The rules that matter most:

• Add acid to water, never water to acid. Pentair’s and CircuPool’s manuals and Hayward’s troubleshooting guide all say so.
• Never let acid meet chlorine. CDC says mixing chlorine products with acid “could create toxic gases,” and its storage poster says to separate acid and chlorine.
• Dose from the container’s label. Don’t borrow a dose from a different product or a chart for another strength.

How to raise pH: soda ash

Soda ash (sodium carbonate) is the MAHC-listed chemical for raising pH. HTH Pool Care pH Up (SKU 67058, 4 lb; a labeled Amazon search) is 99% sodium carbonate. HTH says to add it while the pump is running when pH is below 7.2, and to “not exceed a pH of 7.8, as cloudy water and scale formation may result.” HTH’s web page gives two different amounts for the same pH, so use the dose printed on the container.

Salt pools tend to run high instead. CircuPool’s manual says pH in a saltwater pool “tends to stabilize at approximately 7.8,” and that pH above 7.8 can “drastically reduce the effectiveness of the chlorine.” If pH keeps rising, CircuPool suggests having a pool professional check whether high calcium hardness or total alkalinity is the cause.

Step by step

1. Test pH and total alkalinity. CDC recommends a DPD test kit and calls test strips “less accurate.” The test kit list compares both.
2. Fix alkalinity first, then pH.
3. Pick the chemical: acid to lower, soda ash to raise, baking soda for low alkalinity.
4. Read the whole label and find the dose for your pool volume and reading.
5. Put on goggles and gloves and open one container at a time, as CDC’s poster advises.
6. Add it as the label directs, with the pump running. Pre-dissolve only if the label says to, and then add the chemical to water.
7. Keep pH and chlorine treatments apart. HTH says to wait 4–6 hours after shocking before adding pH Down.
8. Retest after the label’s wait time before adding more.

Store acid away from chlorine products. The chlorine tablet storage guide covers separation in more detail.

Sources

• CDC: Home Pool and Hot Tub Water Treatment and Testing
• CDC: Use Pool Chemicals Safely poster and Store Pool Chemicals Safely poster
• CDC: 2024 Model Aquatic Health Code and annex
• Pentair IntelliChlor Plus and LT installation and user’s guide
• Hayward AquaRite owner’s manual and AquaRite troubleshooting guide
• CircuPool CORE Series manual
• HTH Pool Care pH Down , pH Up and Alkalinity Up

Facts were checked against these sources on October 9, 2026. This guide summarizes published guidance and labels; it is not based on hands-on testing.

FAQ

What is the best way to lower pool pH?

Add an acid. Muriatic (hydrochloric) acid and sodium bisulfate, sold as dry acid, are both on the MAHC’s list of approved pH chemicals, and both lower total alkalinity as well. If you have a salt system, Pentair and CircuPool say never to use dry acid, and Hayward discourages it.

What raises pool pH?

Soda ash (sodium carbonate), which the MAHC lists as an approved pH chemical. HTH pH Up, for example, is 99% sodium carbonate. Baking soda (sodium bicarbonate) is the chemical the MAHC annex names for raising total alkalinity.

Should I adjust alkalinity or pH first?

Alkalinity first. HTH’s pH Down directions say to adjust total alkalinity first to help prevent pH drift, and the MAHC annex explains that low alkalinity lets pH swing quickly while high alkalinity makes pH hard to adjust.

What pH should a pool be?

CDC and the MAHC give 7.0 to 7.8. PHTA’s range, as listed in Pentair’s manual, is 7.4 to 7.6 ideal and 7.2 to 7.8 at the limits. Hayward’s manual gives 7.2 to 7.6, and CircuPool’s gives 7.2 to 7.8 with 7.5 as best.

Can pool acid and chlorine be used together?

Never mix them. CDC warns that mixing chlorine products with acid could create toxic gases. HTH says to wait 4 to 6 hours after shocking before adding its pH Down.