pH decreaser and increaser
Most hot tub "pH down" is dry acid (sodium bisulfate); "pH up" is soda ash. Both also move alkalinity. If pH keeps rising every day, lower alkalinity toward 50 ppm and it will hold steadier.
Hot tub pH and alkalinity calculator
Adjust alkalinity first, to about 50 to 80 ppm, then pH to about 7.4 to 7.6. Hot tub pH drifts up quickly because jets and heat drive carbon dioxide out of the water.
Hot tub pH and alkalinity calculator
Add
0.4oz
of Dry acid / pH minus (sodium bisulfate 93%)
11 gabout 2 tsp by volume
Lowers pH from 7.9 to 7.5 in 400 gal at TA 80.
- Side effects: TA −2.9 ppm.
- Run the jets with the lid open and wait at least 15 minutes (20 after pH decreaser) before anyone gets in.
- Never add acid and chlorine together or in the same spot: mixing them releases toxic chlorine gas. Let the first one circulate before adding the other (the wait is shown on each step).
- Pour it slowly in front of a return jet with the pump running.
- Retest after the water has circulated.
Check the product label. Strengths vary by brand, so enter the % printed on yours. Add one chemical at a time, into the water, and never mix chemicals.
Save this test and get a reminder before your next soak.
Spa Calc for iPhoneComing soon to the App StoreQuestions
Why does my hot tub pH keep going up?
Jets and heat drive out carbon dioxide, which raises pH. Lower alkalinity slows it down.
What should hot tub alkalinity be?
About 50 to 80 ppm.