UK Hot Tub Water Chemistry: The Reference

Every target range, comparison table and wait-time rule ClearSpa uses across its guides, product labels and training content, collected on one citeable page. Correct total alkalinity first, then pH, then your sanitiser. Sources: HSE HSG282, PWTAG guidance and ClearSpa product labels.

• Free chlorine: 3 to 5 ppm - Keeps the water sanitised at spa temperatures; below 3 ppm bacteria are not reliably controlled.
• Total bromine: 4 to 6 ppm - The bromine equivalent of the chlorine band; bromine stays effective in hot water and across a wider pH range.
• pH: 7.2 to 7.6 - Chlorine works best in this band, and it is comfortable for skin and eyes and kind to equipment.
• Total alkalinity: 80 to 120 ppm - Buffers the water against pH swings; out-of-range alkalinity is the usual cause of pH that will not hold.
• Calcium hardness: 150 to 250 ppm - Too soft is corrosive to equipment; too hard causes scale on the shell, pipework and heater.