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. 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. 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. 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. 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.
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.