Setting the water balance: alkalinity, pH, hardness and disinfection
Target values and the correct order for hot tub water: first alkalinity, then pH, then disinfection. With testing methods, dosing rules and common mistakes.
- water balance
- pH
- alkalinity
- chlorine
- testing
Short answer: always work in the same order: first total alkalinity (80 to 120 ppm), then pH (7.2 to 7.6), only then disinfection. Alkalinity is the buffer that keeps the pH stable; skip it and you end up endlessly dosing pH-minus and pH-plus. Measure with fresh test strips or a digital tester, dose small amounts with the pump running, and only measure again after 30 minutes of circulation. With the weekly AquaFinesse rhythm, you then only need to measure at the start, after topping up and when there are complaints.
The target values
| Value | Target range | What goes wrong outside the range |
|---|---|---|
| Total alkalinity (TA) | 80 to 120 ppm | too low: pH fluctuates; too high: pH is difficult to lower and limescale forms |
| pH | 7.2 to 7.6 | too low: corrosion, sealant edges and metal are attacked; too high: disinfection works poorly, limescale, skin irritation |
| Calcium hardness | approximately 150 to 250 ppm | too low: aggressive water; too high: limescale build-up on the element and waterline |
| Free chlorine (if using chlorine) | 1 to 3 ppm | too low: bacterial growth; too high: smell and irritation |
| With AquaFinesse | tablet in the dispenser, weekly liquid | skipping the liquid: biofilm returns |
How to measure
- Test strips: quick and accurate enough for pH and alkalinity. Dip briefly, wait the indicated time, compare in daylight. Store strips dry and closed; damp strips give false readings.
- Digital tester: more accurate for pH; calibrate it periodically according to the manual.
- Where and when: take water at elbow depth, not from the surface, and measure at least 30 minutes after the last dose.
- Fill water: also measure the hardness immediately after filling; in parts of the Netherlands, tap water is hard, and that determines how prone to limescale your bath is.
Setting it step by step
- Test TA, pH and hardness of the fresh water.
- Set the alkalinity first. Too low: increase it with an alkalinity increaser (or sodium bicarbonate), in small portions. Too high: lower it with pH-minus in small portions and let it circulate; TA slowly drops along with it.
- Then set the pH. Lower it with pH-minus, raise it with pH-plus. Dose small amounts, let it circulate for 30 minutes, measure again. Large doses in one go always overshoot.
- Bring disinfection up to level. With AquaFinesse: dose the liquid and place the tablet in the dispenser above the filter, briefly run the pump at full power. With chlorine: dose to 1 to 3 ppm free chlorine.
- Wait 30 minutes and measure once more before anyone enters the bath.
Dosing rules that always apply
- Add products to the water, never water to the product.
- Dose with the pump or jets running and the cover open, so fumes can escape.
- Never mix different products together dry; this can cause dangerous reactions.
- Tablets always in a dispenser, never loose on the bottom of the shell.
- Store everything dry, cool, closed and out of reach of children.
When to measure with AquaFinesse
The system keeps the weekly chemistry simple, but does not fully replace measuring. Measure the pH:
- immediately after every fresh fill;
- after topping up more than a few buckets of water;
- after an evening with many bathers;
- in case of smell, foam, cloudy water or skin irritation;
- otherwise once a month as a routine check.
Common mistakes
- Adjusting the pH without first measuring the alkalinity: the pH keeps fluctuating no matter how much you dose.
- Dosing disinfectant at the wrong pH: above 7.8, chlorine barely works.
- Too much in one go: overshooting, then counter-dosing, then overshooting again. Dosing small amounts and waiting is faster.
- Measuring immediately after dosing or from the water surface: gives a distorted picture.
- Old or damp test strips: replace them every season.
- Foam suppressant as a solution for foam: foam is a symptom of contaminated or unbalanced water; see fixing cloudy water.
Frequently asked questions
What pH value should hot tub water have?
How long should I wait after adding chemicals?
Why does my pH keep fluctuating?
Do I still need to measure the water balance with AquaFinesse?
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