Hot tub water care during a hire: testing, chlorine and common problems

Updated 6 November 2026 · By the Hot Tub Hire team

Short answer: During a hot tub hire, test the water at least once a day with the strips supplied, keep the sanitiser in the supplier's target range, often 3 to 5 mg/l free chlorine or 4 to 6 mg/l bromine, and keep pH around 7.2 to 7.6. Top up sanitiser after heavy use, rinse the filter every few days, shower before use and keep the cover on. Cloudy or foamy water usually means the sanitiser is low or the filter needs cleaning.

Hot tub water care during a hire: testing, chlorine and common problems

Why water care matters

Warm water is ideal for bacteria, and every bather adds sweat, skin cells, cosmetics and body oils. The sanitiser, usually chlorine or bromine, kills germs and breaks down this waste, but it is used up quickly, especially in a small volume of water at 38°C with several people in it. Legionella bacteria can also grow in poorly maintained hot tubs and spread through the spray and bubbles, which is why daily testing is important.

Water care also protects the tub and your comfort. Water that is out of balance can sting eyes, irritate skin, smell strongly and leave scale on the heater, and a neglected tub can turn cloudy within a day in warm weather. A few minutes of testing and dosing each day prevents almost all of these problems.

Target levels

Test	Typical target	What it does
Free chlorine	3 to 5 mg/l	Kills germs and breaks down waste
Bromine (if used instead of chlorine)	4 to 6 mg/l	An alternative sanitiser, more stable at high temperatures
pH	7.2 to 7.6	Keeps the sanitiser working and the water comfortable on skin and eyes
Total alkalinity	Around 80 to 120 mg/l	Steadies the pH so it does not swing

Always follow the supplier's instructions and target ranges for the tub and chemicals provided. Commercial hot tubs in holiday lets follow HSE guidance HSG282, which uses free chlorine of 3 to 5 mg/l or bromine of 4 to 6 mg/l and pH of 7.0 to 7.6.

Test strips give a quick reading that is accurate enough for a domestic hire. Commercial operators usually use more precise liquid or tablet test kits or electronic photometers, as their records need to be reliable. Whatever you use, test before adding chemicals so you know what the water needs, rather than dosing by habit.

A simple daily routine

Test the water each morning and again before an evening session
Add sanitiser if free chlorine or bromine is below the target
Adjust pH only after the sanitiser is in range, using small doses
Run the filter pump with the cover off for a few minutes after adding chemicals
Top up sanitiser after a busy session
Rinse the filter cartridge every two to three days
Keep the cover on and fastened between uses

Add chemicals one at a time, never mix them together, and store them dry and out of reach of children. Measure doses rather than guessing, and read the labels.

If the tub will not be used for a day or two during the hire, keep the cover on, leave the filter running as the supplier advises and still check the sanitiser, as it continues to break down in warm water even without bathers.

Common problems and fixes

Problem	Likely cause	What to do
Cloudy water	Low sanitiser, dirty filter or high pH	Test, add sanitiser, rinse the filter, then retest
Foam on the surface	Soap, lotions or residue from swimwear	Rinse off before use, skim foam, check sanitiser
Strong chlorine smell	Used-up chlorine combining with waste	Shock dose as instructed and check free chlorine
Itchy skin or red eyes	pH or sanitiser out of range	Test and correct, and shower after use
Green or slimy surfaces	Sanitiser too low for too long	Stop using the tub and contact the supplier

If the water stays cloudy, smells unpleasant or the tests will not come into range after treatment, stop using the tub and contact your supplier. Do not keep adding chemicals.

Shock dosing

A shock dose is a larger dose of sanitiser or a non-chlorine oxidiser used to burn off waste that builds up after heavy use. It is often recommended after a party or every few days during a busy hire. Leave the cover off while shocking, keep everyone out until levels return to the normal range, and follow the dose on the product label.

Chlorine-based shock and non-chlorine shock both have their place. Non-chlorine shock removes waste without raising chlorine levels much, so the tub can be used again sooner, while chlorine shock also sanitises. Use the product the supplier provided, and ask before adding anything you have bought yourself, as some chemicals do not mix well.

Helping the water last

Shower or rinse before getting in
Avoid lotions, fake tan and make-up in the tub
Rinse swimwear in clean water rather than washing it in detergent
Keep food, drink and pets out of the water
Do not exceed the tub's rated number of bathers

If you are unsure about a test result, test again with a fresh strip in good light, holding it level and reading it at the time stated on the container. Strips that have been left open to damp air can give false readings, so keep the lid tightly closed.