How to lower pH in a hot tub
Adding pH down (sodium bisulfate) with jets on is how to lower pH in hot tub water. After 15 minutes, test again and stop once you reach 7.4 to 7.6.
Select your tub and current pH reading to find the right amount of pH down.
- Ideal hot tub pH
- 7.4 to 7.6
- Bring it down before anyone soaks
- 8.0 or higher
- pH down for each 100 gallons of water
- 0.1 to 0.2 oz
- Run the jets before testing again
- Allow 15 min
Calculator for pH down doses based on tub size
Since 7.8 remains safe, that column offers an optional top-up to reach the ideal 7.4 to 7.6. If the reading hits 8.0 or more, reduce it before anyone enters the water.
These doses come from the Leslie's spa dosage chart, adjusted for each tub size. Every dose tries to reach about 7.5.
| Tub size | pH 7.8 (still OK) | pH 8.0 | pH 8.2 or higher |
|---|---|---|---|
| 180 gal (670 L) | 0.2 oz (5 g) | 0.3 oz (9 g) | 0.4 oz (10 g) |
| 250 gal (930 L) | 0.3 oz (7 g) | 0.4 oz (12 g) | 0.5 oz (14 g) |
| 290 gal (1,100 L) | 0.3 oz (8 g) | 0.5 oz (14 g) | 0.6 oz (16 g) |
| 350 gal (1,330 L) | 0.3 oz (10 g) | 0.6 oz (17 g) | 0.7 oz (20 g) |
| 500 gal (1,900 L) | 0.5 oz (14 g) | 0.9 oz (24 g) | 1 oz (28 g) |
Leslie's lists no values higher than 8.2. If you see 8.4 or darker, use the 8.2 dose, then test after waiting. Apply a second dose if needed.
According to Leslie's, a teaspoon is about 0.17 oz (5 g) and a kitchen tablespoon about 0.5 oz (14 g). Unsure of your tub size? Calculate it using how many gallons is my hot tub.
Steps for handling pH at 8.4
Since 8.4 is the darkest block on the AquaChek color chart, actual pH could be higher. Because the Leslie's chart ends at 8.2, begin with the 8.2 dose and retest.
- Start by checking alkalinity. pH keeps getting pushed back up when the test shows more than 120 ppm (parts per million), so deal with alkalinity first and lower it.
- Put the first dose in while jets run. Use the pH down chart here or the calculator for your specific size.
- After 15 minutes, test again. Add the same dose again if the strip still shows 8.4.
- Stop once you reach 7.4 to 7.6. Several small doses are easier to manage than one large one.
| Tub size | First pH down dose at 8.4 | In kitchen spoons |
|---|---|---|
| 200 gal (760 L) | 0.4 oz (11 g) | About 2.5 teaspoons |
| 300 gal (1,140 L) | 0.6 oz (17 g) | About 1 tablespoon |
| 400 gal (1,510 L) | 0.8 oz (23 g) | About 1.5 tablespoons |
Per 500 gallons (1,890 litres), the AquaChek guide limits dry acid to 1 oz (28 g) at one time.
Step-by-step guide for adding pH down
- Begin with a test. Use the test strip guide to read the pH and alkalinity pads.
- Start with alkalinity if readings exceed 120 ppm. High alkalinity keeps pH high, so lower the alkalinity before fixing pH.
- Measure out the dose. Refer to the chart, or try the chemical calculator for different readings.
- Switch on the jets. According to the American Whirlpool manual, you should add pH adjusters while the jets run.
- Spread it over the top of the water. If you need a larger amount, AquaChek's water care guide suggests dissolving the dry acid in a plastic bucket filled with tub water first.
- Let it sit for 15 minutes, then test again. Before adding more chemicals, allow 15 minutes for circulation, according to Leslie's.
- Stop once you reach 7.4 to 7.6. Hot Spring waits two hours for the final reading because early tests can be wrong.
Add products one at a time, and never mix two chemicals in a scoop or bucket. Because dry acid is corrosive, keep it away from children and wear eye protection.
Reasons your hot tub pH keeps rising
Bather load, new water, added chemicals, and sanitizer type affect pH, per the Hot Spring owner's manual. One cause usually explains a rise that keeps happening.
| Cause | What you notice | What to do |
|---|---|---|
| High alkalinity | pH creeps back up after each dose | Lower alkalinity to 80 to 120 ppm |
| Fill water with a high pH | A fresh fill or top-up reads high | Test after every top-up |
| Lotion, makeup and body oils | Readings climb after busy soaks | Test more often when the tub is busy |
| Old water | Dissolved solids build up over months | Drain and refill |
| New chemicals or a sanitizer change | Readings jump after you add something | Retest after each chemical |
Lay-Z-Spa identifies lotions, hard water with high pH, and old water as sources of high alkalinity. Hot Spring points out that high alkalinity holds pH high and makes it hard to lower.
Hot tub pH too high: what you will see
Cloudy water is often the first warning sign. American Whirlpool states that pH above 7.8 causes cloudiness and scale buildup on the shell and equipment. The filter also suffers from high pH.
Chlorine does not work as well either. The CDC says chlorine cannot kill germs as well when pH rises, especially above 8.0. Lay-Z-Spa adds that chlorine levels swing and skin or eyes get irritated.
If water remains hazy after fixing pH, follow the steps for cloudy hot tub water.
How to lower pH in hot tub naturally
Manuals from spa manufacturers list no fix without chemicals. Hot Spring, Lay-Z-Spa and AquaChek each name the same fix: pH down, which is sodium bisulfate.
Fresh water is the only way to go without pH down. Hot Spring points out that new water alters pH and alkalinity. A partial drain and refill may help, yet this works only if hose water tests lower. Test a glass of hose water with a strip first.
Old water presents a different issue. If water has sat for months, a full drain and refill removes the buildup causing stubborn high readings.
Is vinegar an option for lowering hot tub pH?
You can do it, though it is not wise. According to PubChem, vinegar is acetic acid, which is a weak acid. You will need quite a bit: Swim University estimates about 1/2 cup (118 ml) for every 100 gallons (380 litres).
Swim University adds that vinegar varies in strength across bottles, and no chart lists doses for it. That means you would be guessing every time. Instead, use pH down (sodium bisulfate), the product named by Hot Spring, Lay-Z-Spa and AquaChek, and follow the pH down chart for dosing.
How much muriatic acid should go into a hot tub or spa?
Hydrochloric acid also goes by the name muriatic acid, per the Intex spa manual. Pool stores sell it at roughly 31% strength, according to the CPO dosage study.
Concentrated muriatic acid is not recommended for spas in the AquaChek guide. It is so strong that measuring the tiny amount a hot tub needs is hard.
That's why the calculator here works with dry acid (sodium bisulfate), the product sold as pH down, and it offers no dose of muriatic acid. Instead, rely on the pH down dose found in the chart.
AquaChek warns that both muriatic acid and dry acid are highly corrosive. Add acid to water, never water to acid; wear eye protection; never mix with chlorine or other chemicals.
Common questions
What pH level counts as too high for a hot tub?
Any value over 7.8 exceeds the spa limit found in the NSPI standard reprinted by AquaChek. Your goal is 7.4 to 7.6; use pH down once the strip hits 7.8 or higher.
Why does the pH in my hot tub keep rising?
The most common cause is high alkalinity. Since this keeps pH high, first drop alkalinity to 80 to 120 ppm, then dose for pH again.
Does pH down reduce alkalinity as well?
Yes. Hot Spring markets it as pH/Alkalinity Down because sodium bisulfate lowers both. Check both pads following every dose.
How long must I wait to use the hot tub after adding pH down?
Run the jets at least 15 minutes before testing. Lay-Z-Spa says to soak only after alkalinity, pH and chlorine return to range.
Are there dangers when pH is high in a hot tub?
Weaker chlorine is the main risk, letting germs live longer, says the CDC. High pH can also irritate eyes and skin while leaving scale on the shell and heater.