Hot Tub Water Testing Guide
Testing is the one hot tub job everything else depends on. Without a reading you are guessing, and guessing with spa chemicals is how water ends up cloudy, itchy, or hard on your equipment. This guide covers the ways to test, what the numbers usually mean, and a routine that keeps it to a couple of minutes.
Test strips we use
Multi-pad strips read pH, sanitizer, alkalinity and hardness in one dip. Check the pads match your sanitizer (chlorine or bromine).
See test strips on Amazon → Our picks →As an Amazon Associate, HTReminder earns from qualifying purchases.
Ways to test, compared
| Method | Good at | Watch out for |
|---|---|---|
| Test strips | Fast, cheap, no mixing; fine for everyday checks | Color reading is subjective; strips go off with moisture and age |
| Liquid / drop kits | More precise, best for troubleshooting | Slower; reagents expire; takes some practice |
| Digital testers | No color guessing | Cost, calibration, batteries |
| Store water test | A second opinion and metals testing | A trip, and the sample changes on the way |
Most owners use strips day to day and a liquid kit or a store test now and then to confirm the strips are telling the truth.
What to test and the usual ranges
These are the ranges most spa makers and test-kit makers publish. Your tub's manual and your product labels come first if they say something different.
| Reading | Usual range | How often |
|---|---|---|
| pH | 7.2 – 7.8 | Before you soak |
| Free chlorine (chlorine tubs) | about 1 – 3 ppm (some labels say up to 5) | Before you soak |
| Bromine (bromine tubs) | about 3 – 5 ppm | Before you soak |
| Total alkalinity | 80 – 120 ppm | Weekly |
| Calcium hardness | roughly 150 – 250 ppm | Weekly to monthly |
| Total dissolved solids | rising steadily = water is getting old | Monthly, if you have a meter |
Not sure what a color means? The test strip color chart walks through every pad, and how to read test strips covers the technique.
Getting an accurate strip reading
- Dry hands, sealed bottle. Moisture ruins the strips left in the bottle.
- Jets off. Test still water from about elbow depth, away from where you just added anything.
- Don't shake the strip. Hold it level and read it at the time the label says, usually 15–30 seconds.
- Good light. Daylight or a bright white light, never a yellow bulb at night.
- Wait after adding chemicals. A reading right after a dose is not your real number; follow the product label on wait times.
- Watch the date. Old strips drift even before the printed expiry once the bottle has been opened a lot.
Using pool strips? They mostly work in a hot tub, with a couple of catches: can you use pool test strips in a hot tub.
What the readings tell you
pH
Low pH (acidic) water can sting and slowly corrodes metal parts like the heater. High pH makes sanitizer work less well and tends toward cloudy water and scale.
Sanitizer
Below range, germs can grow; above range, water can irritate skin and eyes. If it is high, wait and retest before soaking. After a shock, see how long to wait after shocking.
Alkalinity
Alkalinity is the buffer that holds pH steady. When it is low, pH bounces around; when it is high, pH tends to creep up.
A simple routine
- Before each soak: quick strip for pH and sanitizer.
- Weekly: full strip including alkalinity and hardness; rinse the filter.
- Monthly: confirm with a liquid kit or a store test; note how old the water is.
- After a refill or a problem: a store test, including metals.
Picking strips? See our comparison of the best hot tub test strips.
Let your phone read the colors
HTReminder reads a test strip from a photo, keeps your history so you can see trends, and reminds you when it is time to test. You still choose what to add — the app just takes the guesswork out of the colors.
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