Short answer: the Sanitizing Spa Stick is a mineral cartridge you drop on the bottom of a cold plunge, priced at $27.99. Renu says it helps control algae and bacteria and lasts about 3 months. It supports your filter and sanitizer. It doesn’t replace them.
Run the numbers
One stick lasts about 3 months, so you need 4 a year. That is about $112 a year, or $9.33 a month. It is one of the cheaper parts of running a cold plunge.
How does it work?
The listing says natural minerals react with the water to help control algae and bacteria. Renu doesn’t publish the mineral composition in detail. Mineral sanitizers for spas commonly use silver or copper, but I can’t confirm what is in this one. Ask Renu if you want to know, or if anyone using the tub has a metal sensitivity.
Is it enough on its own?
No, and Renu doesn’t claim it is. A mineral stick slows growth. It doesn’t oxidize the oils and sweat that people bring into the water, and it doesn’t filter out debris. You still need:
- A working filter, changed on schedule
- An oxidizer or sanitizer, dosed as the maker directs
- Test strips to check the result
- A full water change at intervals
Cold water slows bacterial growth, but it doesn’t stop it. Cloudy water, a slick feel on the walls, or a smell means the water needs attention, whatever the stick is doing.
How do you use it?
Drop it on the bottom of the tank. There is no measuring or mixing. Write the date on your calendar and replace it after 3 months. It keeps working whether or not you remember it, which is its appeal.
Will it work in other tubs?
It is sold for Renu’s tubs. Our data doesn’t state a water volume it is sized for. Renu’s Cold Stoic holds about 95 gallons, so a much larger tub may need a different approach. Ask Renu before using it elsewhere.
How it compares
The Renu Pure Water Treatment Kit is the full liquid approach at $75. Cold Plunge Sanitizer: Mineral Stick or Full Kit? compares them. Our button goes to Renu Therapy’s product page.
