

Spa water stays safe through a combination of appropriate sanitiser, filtration, circulation, balanced water chemistry and regular testing. There is no single chemical dose or maintenance schedule that suits every spa, water source and sanitising system.
Follow the instructions for the exact sanitiser and spa system. Chlorine, bromine and other approved systems have different operating requirements and should not be mixed or substituted without checking compatibility.
Test the water parameters required by your chosen system and adjust them according to the product label and spa instructions. Bather load, water temperature, spa volume and source-water chemistry can all change what treatment is required.
pH and total alkalinity influence water comfort, sanitiser performance and the risk of scale or corrosion. Use the target ranges specified by the current chemical system and spa guidance rather than relying on an old universal number copied from an article.
Shock or oxidising products can be used as part of some water-care systems to manage accumulated organic contaminants. The correct product, dose, circulation time and re-entry period depend on the exact chemical label and sanitising programme.
Where a spa is equipped with ozone or UV, treat it as part of the broader water-care system. Neither technology should be assumed to replace sanitiser, routine testing or filtration. Read the Ozone & UV Guide.
Do not assume one cause. Check sanitiser, pH and other required water-balance parameters, filtration, filter condition, bather load and contamination from body products. If the water cannot be returned to a safe condition using the relevant product instructions, draining and refilling may be appropriate.
Spa Maintenance Guide · Spa pH Guide · How to Shock a Spa · Evidence Centre
Updated: 25 August 2026.
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