Run the pump, take a sample about 30 cm below the surface, dip a test strip for 15 seconds and compare it promptly. Aim for chlorine 3-5 mg/l or bromine 4-6 mg/l, pH 7.2-7.6 and alkalinity 80-120 mg/l. Test two to three times a week and retest 20-30 minutes after dosing.
How to test hot tub chemicals in five minutes: dip a strip 2-3 times weekly and hold chlorine 3-5 mg/l or bromine 4-6 mg/l, pH 7.2-7.6, TA 80-120 ppm.
Testing hot tub chemicals takes less than five minutes: dip a test strip at elbow depth, wait 15 seconds, and compare the pads against the chart. You are looking for free chlorine of 3–5 mg/l (or bromine 4–6 mg/l), pH between 7.2 and 7.6 and total alkalinity of 80–120 ppm.[1] Do this 2–3 times a week and before bathing after any break, and you will catch every water problem while it is still a cheap, one-scoop fix. Here is the full routine UK spa owners should follow.
For weekly home testing, one of these two options covers everything:
Store strips with the lid tight, in a cool dry place, and bin them after the expiry date – damp or expired strips read low and will have you chasing problems that do not exist.
| Parameter | Target | If low | If high |
|---|---|---|---|
| Free chlorine | 3–5 mg/l | Dose chlorine granules | Leave lid off, retest before use |
| Bromine | 4–6 mg/l | Top up tablets/granules | Pause dispenser, retest |
| pH | 7.2–7.6 | Add pH plus | Add pH minus |
| Total alkalinity | 80–120 ppm | Add TA increaser | Small acid doses, retest |
Always correct in order: alkalinity first, then pH, then sanitiser.[2] Use pH & alkalinity reducer to bring high readings down in small doses, retesting 20–30 minutes after each addition with the pump running.
Strips and DPD1 tablets measure free chlorine – the portion still available to kill bacteria. Total chlorine includes the spent, combined form that causes the classic \"chlorine smell\" and eye sting.[3] If total reads noticeably higher than free, the gap is combined chlorine and the water needs a shock dose to burn it off. Our guide to free vs total chlorine explains how to read and act on the difference.
Move to daily testing after a water change (fresh fills drift fast for the first week), during heavy use or hot weather, and whenever you are treating a problem. Hot tubs run at up to 40°C, and warm water consumes sanitiser far faster than a pool – a spa that tested fine on Monday can be at zero by Friday.[1] Testing is also the habit that makes every other bit of maintenance work; see the benefits of regular water testing for why it pays for itself.
At least 2–3 times a week, before bathing after any gap of a few days, and daily after a refill or while correcting a problem. Testing takes five minutes and prevents almost every expensive water issue.
Free chlorine 3–5 mg/l or bromine 4–6 mg/l, pH 7.2–7.6 and total alkalinity 80–120 ppm. Keep water temperature at 40°C or below.[1]
Yes, for home use – fresh, properly stored strips are accurate enough to keep water safe. Tablet or photometer testing adds precision if you run a holiday let or want exact numbers, and is the standard for commercial compliance.
Either the dose has not circulated yet – run the pump 20–30 minutes and retest – or the water has a high chlorine demand from organic waste, in which case it is consuming sanitiser as fast as you add it. A shock dose usually resets the balance.
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