Balanced spa water means pH 7.2-7.6, alkalinity 80-120 ppm and a steady sanitiser level. The UK targets, the order to adjust in, and mistakes to avoid.
Balanced spa water means holding four numbers in range: pH 7.2–7.6, total alkalinity 80–120 ppm, sanitiser at 3–5 mg/l free chlorine or 4–6 mg/l bromine, and calcium hardness around 100–200 mg/l. Test two to three times a week, fix alkalinity before pH, and make one adjustment at a time – that routine prevents almost every common UK hot tub water problem, from cloudy water to corroded heaters.
| Parameter | Ideal range | What it does |
|---|---|---|
| pH | 7.2–7.6 | Keeps water comfortable, protects equipment and lets sanitiser work at full strength |
| Total alkalinity | 80–120 ppm | Buffers pH so it does not swing after every soak or dose |
| Free chlorine | 3–5 mg/l | Kills bacteria (use bromine at 4–6 mg/l instead if that is your sanitiser) |
| Calcium hardness | 100–200 mg/l | Stops soft water attacking metal parts and hard water scaling them |
Test with 6-in-1 test strips two to three times a week and before every soak after a break. Strips read all four parameters in seconds, which is accurate enough for routine home care.
Total alkalinity is the buffer that holds pH steady. When it is low, pH lurches up and down after every bather and every dose; when it is high, pH drifts upwards and resists correction. That is why the golden rule of balancing is: correct total alkalinity first, let the water circulate, then adjust pH. Chasing pH while alkalinity is out of range wastes chemicals and never settles – a pattern explained in why pH chases alkalinity. For the full dosing sequence, follow the water balancing order of operations.
Always dissolve or dose with the pumps running, wait for a full circulation cycle (30 minutes or more) and retest before adding anything else. Small, patient doses beat one big correction every time.
Low pH slowly dissolves heater elements, pump seals and metal fittings, and stings eyes and skin. High pH drops scale onto the shell and heater, clouds the water and cripples chlorine's killing power. Unstable alkalinity makes both problems recur no matter how often you dose. Left unchecked, the bill is not a bottle of balancer – it is a heater or pump replacement, which is why balance matters as much as sanitiser.
Hold pH at 7.2-7.6, total alkalinity at 80-120 ppm, free chlorine at 3-5 mg/l (or bromine at 4-6 mg/l) and calcium hardness at roughly 100-200 mg/l, testing two to three times a week.
Always correct total alkalinity first. Alkalinity is the buffer that holds pH steady, so once it sits at 80-120 ppm the pH usually settles close to range and any remaining adjustment holds properly.
Low pH corrodes heaters, seals and fittings and irritates skin and eyes; high pH causes scale, cloudy water and weak sanitiser performance. Over time unbalanced water leads to expensive equipment failure, not just poor bathing conditions.
Test two to three times each week during normal use, before bathing after any break, and around 30 minutes after any chemical adjustment so you can confirm the dose worked before adding anything else.