How to select hot tub chemicals: pick bromine or chlorine, add shock, pH and alkalinity adjusters and test strips - with UK target levels for each.
Selecting hot tub chemicals is a five-item shopping list: a sanitiser (bromine or chlorine), a shock/oxidiser, pH adjusters, an alkalinity adjuster and test strips. Pick your sanitiser system first – everything else follows from that choice – and buy products designed for spas, not pools. This step-by-step guide walks UK owners through each decision, with the target levels your choices need to hit: free chlorine 3–5 mg/l or bromine 4–6 mg/l, pH 7.2–7.6 and total alkalinity 80–120 ppm.
This is the decision that shapes everything else, because bromine and chlorine products are not interchangeable and should never be mixed dry. Both are approved under the GB Biocidal Products Regulation, so choose on how you use your tub:
Undecided? Our comparison of chlorine vs bromine for UK hot tubs covers the trade-offs in depth.
Sanitiser kills bacteria, but it is the weekly shock that removes the sweat, oils and cosmetics that build up in a small, hot volume of water. A non-chlorine shock works with both bromine and chlorine systems, does not raise sanitiser levels, and usually lets you bathe again after 15–20 minutes of circulation – which is why it is the default choice for most spa owners.
Every tub eventually needs all three, so buy them up front rather than at 9pm when a test reads wrong:
In hard-water areas of the UK, add a scale inhibitor to the list; in soft-water areas, a calcium hardness increaser.
Testing is not an accessory – it is the product that makes every other product work, because you cannot dose what you cannot measure. 6-in-1 test strips cover sanitiser, pH, alkalinity and hardness in one dip and are the right starting point for almost everyone. Plan to test 2–3 times a week.
If you are starting from an empty cupboard, a matched kit is cheaper and simpler than assembling the list yourself – a bromine starter kit or chlorine starter kit bundles the sanitiser, shock, balancers and testing that work together. Buying piecemeal makes more sense once you know your tub's habits and just need to restock the products you actually consume.
Five things: a sanitiser (bromine or chlorine), a shock/oxidiser, pH plus and minus, an alkalinity increaser and test strips. A starter kit bundles all of them in matched formulations.
Yes, but only at a water change: drain, rinse the shell and filter thoroughly, and refill before switching systems. Never mix bromine and chlorine products dry – they react dangerously.
Judge on the active ingredient and concentration, not the price tag. A cheaper tub of the same active at the same strength is fine; an unlabelled product with no BPR statement or dosing table is a false economy.
A typical UK family tub gets through sanitiser fastest, followed by shock, with balancers a distant third. Usage rises sharply in summer and with bather load – warm water at up to 40°C consumes sanitiser far faster than a pool.