A full water routine means dosing two liquids and reading test strips. A drop-in stick promises to skip all that.
This article compares the two approaches using Renu Therapy’s products. For the wider accessory list, start with the cold plunge accessories buying guide.
Short answer: if your tub has built-in ozone and filtration, a mineral stick is the simple option. Choose the full kit if you want to measure and adjust the water yourself.
Side by side
| Sanitizing Spa Stick | Pure Water Treatment Kit | |
|---|---|---|
| Price | $27.99 | $75 |
| What’s in it | One mineral stick | Sanitizer (16 fl oz), oxidizer (32 fl oz), 25 test strips |
| How you use it | Drop it on the bottom of the tank | Dose at each fill, then weekly |
| Lasts | About 3 months | Depends on dosing |
| Testing | None | Strips included |
From Renu Therapy listings, checked September 2026.
What the stick does
Renu Therapy says the stick uses natural minerals to help control algae and bacteria, and that it helps extend filter life. You place it on the bottom of the tank and leave it for about 3 months.
Here’s what the spec sheet won’t tell you: Renu’s own pages describe it two ways. One says “natural minerals,” another says silver ions. The listing in our data doesn’t give the full composition.
You get one step every 3 months. You give up any reading of what’s in the water.
What the kit does
The kit is a manual routine. Its published directions: 2 teaspoons of sanitizer and 2 teaspoons of oxidizer at each fill, then 1 teaspoon of oxidizer a week, with sanitizer added as the strips call for it.
You get control and a way to check your work. You give up simplicity, and you pay $75 up front.
Neither replaces the filter
Renu Therapy says its tubs’ ozone generator and filter remove the need for chemicals. It sells both products as options on top of that system.
So the base routine stays the same either way: change the filter every 2 to 6 weeks, as Renu’s FAQ says.
Run the numbers
- Sticks for a year: 4 x $27.99 = $111.96
- One kit: $75, and how long it lasts depends on how often you refill and dose
At 1 teaspoon of oxidizer a week, a 32 fl oz bottle holds far more than a year of weekly doses. The 25 strips run out first, at about 6 months of weekly tests.
Which to pick
My rule of thumb: pick the routine you’ll keep. A stick you replace on time beats a kit that sits in the garage.
Choose the kit if several people share the tub, or if the water has already gone cloudy once. Choose the stick for one or two users on a filtered tub.
If you haven’t bought a tub yet, the cold plunge buying guide is the place to start.
Bottom line: the stick is easier, the kit is more precise, and the filter matters more than either.
Sources
- Renu Therapy, Sanitizing Spa Stick and Pure Water Treatment Kit listings (price, contents, dosing, lifespan), checked September 2026
- Renu Therapy FAQ (ozone system, filter interval, stick lifespan), accessed October 8, 2026: renutherapy.com