How to read hot tub test strips

To read a hot tub test strip, dip it elbow deep for about 2 seconds, pull it out, hold it level without shaking, and compare each pad to the color chart on the bottle at the time printed on the label, usually 15 seconds. You want pH 7.2 to 7.8, total alkalinity 80 to 120 ppm, free chlorine 1 to 3 ppm or bromine 3 to 5 ppm, and calcium hardness 150 to 250 ppm.

How to use a test strip, step by step

1. Run the jets for a minute. Then turn them off. You want mixed water, not bubbles on the strip.
2. Dry your hands. Take out one strip and close the bottle right away. Do not touch the pads.
3. Dip to elbow depth. Surface water gives odd readings. Hold the strip under for about 2 seconds, or whatever your bottle says.
4. Remove it and hold it level. Pads facing up. Do not shake off the water. Shaking lets one pad bleed into the next.
5. Read at the stated time. Most brands say 15 seconds. Some pads, such as hardness, may say 30. After about a minute the colors keep changing and no longer mean anything.
6. Read in daylight. Colors are hard to judge under a porch light or a colored spa light.

What each pad means

Pad	What it measures	Target	If it is off
Free chlorine	Chlorine that is available to sanitize	1–3 ppm	Low: add sanitizer. Above 5 ppm: wait before soaking.
Total chlorine	Free chlorine plus used-up (combined) chlorine	Within 0.5 ppm of free chlorine	Much higher than free: shock the tub.
Bromine	Sanitizer level in a bromine tub	3–5 ppm	Low: add bromine or shock to reactivate it.
pH	How acidic or basic the water is	7.2–7.8	Use pH increaser or decreaser per the label.
Total alkalinity	The buffer that holds pH steady	80–120 ppm	Fix this before pH.
Calcium (total) hardness	Dissolved calcium	150–250 ppm	Low: add calcium increaser. High: dilute or use a scale control product.
Cyanuric acid (stabilizer)	Builds up from dichlor chlorine	Roughly 30–50 ppm	Very high: partly drain and refill.

Not every strip has every pad. A basic 4-way strip covers sanitizer, pH, alkalinity, and hardness, which is enough for weekly care. For the full picture on targets, see the ideal levels chart.

What to fix first

Order matters, because each reading affects the next one.

1. Total alkalinity. Get it to 80–120 ppm. If alkalinity is off, pH will not stay put. See how to adjust alkalinity.
2. pH. Bring it to 7.2–7.8. Sanitizer works poorly when pH is high.
3. Sanitizer. Adjust chlorine or bromine last, once pH is in range.
4. Calcium hardness. Check it after each refill. It changes slowly.

Add one product at a time, with the jets running and the cover open. Follow the product label for the dose for your tub's volume. Wait 20 to 30 minutes, then retest before adding anything else. Never mix chemicals together.

Common misreads

• Pad stays white when chlorine should be high. Very high chlorine or bromine can bleach the sanitizer pad so it looks like zero. If you just shocked the tub, wait a few hours and retest.
• pH reads purple or very high after shocking. High sanitizer also throws off the pH pad. Trust the pH reading only when sanitizer is under about 5 ppm.
• Colors between two blocks. Pick the midpoint. A strip is a range tool, not a lab instrument.
• Different result every time. Check the expiry date. Damp strips fail first, often with blotchy or faded pads straight out of the bottle.
• Bromine tub, chlorine strip. A chlorine pad reads bromine at roughly half its real value. Multiply by about 2.25, or buy strips with a bromine scale.

How often to test

Test 2 to 3 times a week with normal use. Test before a party and the morning after one. Test a fresh fill once it is warm, since cold water reads differently and dissolves chemicals slowly. If the water looks dull or smells sharp, test before anyone gets in. A sharp chlorine smell usually means too little free chlorine, not too much, and a shock treatment is due.

Strips versus liquid kits

Strips are fast and good enough for routine checks. Liquid drop kits take a few minutes but give finer steps, which helps when you are chasing a problem such as cloudy water that will not clear. Many owners use strips during the week and a drop kit or store test once a month.

Let the strip reader do the matching

If you find the color blocks hard to tell apart, take a photo of the strip next to the bottle chart and use the AskTub strip reader. It reads the pads and tells you what to adjust first for your tub's size.