How to raise pH in a hot tub
pH up, also known as sodium carbonate or soda ash, is the solution for how to raise pH in hot tub water. Start by checking alkalinity, then add your dose to reach 7.4 to 7.6.
Choose your tub and pH level to find how much pH up you need.
- Best pH level
- 7.4 to 7.6
- pH up for every 100 gallons of water
- 0.13 to 0.5 oz (4 to 14 g)
- Lowest pH the spa standard allows
- 7.2
- Get alkalinity to this point before you change pH
- 80 ppm
If your reading is under 80 ppm, boost alkalinity first.
Alkalinity acts as a buffer that keeps pH stable in water. According to the Intex owner's manual, you should always fix alkalinity before changing pH.
Frog says low alkalinity pulls pH down and allows it to swing. If your alkalinity pad shows less than 80 ppm, raise the alkalinity first. Since baking soda can lift pH a little too, test pH again before adding pH up.
Chart showing pH up doses for your tub
We scaled figures from the Leslie's spa dosage chart to each tub. Every dose targets about 7.5.
| Tub size | pH 7.2 | pH 6.8 | pH 6.5 or lower |
|---|---|---|---|
| 180 gal (670 L) | 0.2 oz (7 g) | 0.7 oz (19 g) | 0.9 oz (26 g) |
| 250 gal (930 L) | 0.3 oz (9 g) | 0.9 oz (26 g) | 1.3 oz (35 g) |
| 290 gal (1,100 L) | 0.4 oz (11 g) | 1.1 oz (30 g) | 1.4 oz (41 g) |
| 350 gal (1,330 L) | 0.5 oz (13 g) | 1.3 oz (37 g) | 1.8 oz (50 g) |
| 500 gal (1,900 L) | 0.7 oz (18 g) | 1.9 oz (52 g) | 2.5 oz (71 g) |
Leslie's chart ends at 6.5. If your reading is 6.2 or lighter, apply the 6.5 dose and test again. Add more if needed.
No chemical name appears on the chart. In its water care guide, AquaChek names soda ash (sodium carbonate) as the thing that raises pH.
Hot tub pH too low: the signs
Water with low pH is acidic. Spa manufacturers list these signs:
- Lay-Z-Spa cites dry, itchy skin and burning eyes.
- Chlorine disappears quickly, forcing you to add more often.
- Metal parts like the heater and pump corrode.
- The Intex manual states that alkalinity drops because acidic water consumes it.
Intex warns that low pH harms the tub and pump, and their warranty excludes damage from chemical imbalance. The CDC notes that pipes corrode more easily when pH falls below 7.0.
How to raise pH in hot tub water, step by step
- Check both pH and alkalinity levels. The test strip guide tells how to read each pad.
- Increase alkalinity first if the level is below 80 ppm. Test pH once more.
- Measure out the pH up product. Check the chart, or use the chemical calculator for your specific tub.
- Pour it in while the jets are on. Add pH adjusters this way, the American Whirlpool manual says.
- Let the jets run for 15 minutes, then test the water. Leslie's permits 15 minutes of circulation between adding chemicals. Hot Spring waits two hours before taking the final pH reading.
- Stop once you reach 7.4 to 7.6. Several small doses are easier to manage than one large one.
Add chemicals one by one, running jets for 15 minutes between doses. Never combine pH up with any other chemical inside one cup or bucket.
Why hot tub pH keeps dropping
Low alkalinity is the most common reason. Rain, sweat, and dirt from soakers drag alkalinity down, says Lay-Z-Spa.
New water, bather load, and added chemicals move pH, adds the Hot Spring manual. Frog checks alkalinity at least twice weekly. This routine spots the drop before your skin feels it.
Common questions
What is the right hot tub pH level?
Target 7.4 to 7.6, which is the ideal in the NSPI spa standard. Under that rule, 7.2 is the minimum while 7.8 is the maximum.
Is baking soda okay for raising pH?
Sodium bicarbonate is the chemical name for baking soda. A CPO dosage study notes it builds alkalinity well yet boosts pH much less than soda ash. Choose this method when pH is fine yet alkalinity dips.
Will adding pH up also boost alkalinity?
It does. Soda ash boosts both pH and alkalinity, so test each pad following a dose. Later, pH might stay high if alkalinity exceeds 120 ppm.
When can I enter the water after adding pH up?
Test the water after running jets for at least 15 minutes. Lay-Z-Spa advises waiting until chlorine, pH and alkalinity are all in range before soaking.
Does a hot tub suffer from low pH?
It does. Intex warranties do not cover corrosion damage to the heater and pump caused by acidic water. It causes chlorine to get used up more rapidly as well.