Short answer: these are 25 test strips that read sanitizer, pH, total alkalinity, and calcium hardness in 10 seconds, for $15. That is 60 cents a test. They tell you whether your water treatment is working, which you can’t judge by eye.
Run the numbers
- 25 strips for $15, or $0.60 each
- Testing once a week: a pack lasts about 6 months
- Testing twice a week: about 3 months
Weekly is a reasonable minimum for a tub in regular use. Test more often after a water change, after heavy use, or when you adjust the dose.
What do the four readings mean?
- Sanitizer: whether there is enough active sanitizer to keep the water clean.
- pH: how acidic or basic the water is. Renu’s target is 7.2 to 7.8.
- Total alkalinity: the water’s resistance to pH change. Renu’s target is 80 to 120 ppm.
- Calcium hardness: dissolved calcium. Too high can leave scale on surfaces and inside the chiller.
Adjust alkalinity first, then pH, because alkalinity holds the pH steady. Cold Plunge Test Strips: How to Read the Results walks through each pad.
How do you get an accurate reading?
Dip the strip, hold it level, and read it at 10 seconds. Colors keep changing after that, so a late reading is wrong. Read it in daylight if you can. Keep the bottle closed and dry: damp strips give false results. Check the expiry date.
Very cold water can slow the color change. If readings look odd, take a cup of water, let it warm for a few minutes, and test that.
What the strips can’t do
They measure. They don’t fix. You need a sanitizer and an oxidizer to act on the results. Strips also won’t detect everything, so change the water on schedule even when the readings look fine.
Do they work with other tubs?
The chemistry is general, so they read any cold plunge or spa water. The target ranges are Renu’s. Check your own tub maker’s recommendations.
How it compares
The same 25 strips come in the Renu Pure Water Treatment Kit with sanitizer and oxidizer for $75. Buy the kit first, then this pack as a refill. Our button goes to Renu Therapy’s product page.
