A cold plunge cleaner is not one product but a system, and getting it wrong is the reason plunge tubs end up unused in garages. Cold water slows biological growth but does not stop it, and a tub without filtration or sanitiser becomes unpleasant within a week or two of regular use.
Filtration is the base layer
A circulation pump through a cartridge filter removes the skin, hair and debris that everything else feeds on. Most chillers include one, which is a large part of what you are paying for. Rinse the cartridge weekly and replace it on the maker's schedule, because a clogged filter stops circulating and the rest of the system quietly stops working with it.
Ozone and UV
Ozone injection and ultraviolet lamps treat water as it passes through the loop, reducing how much chemical sanitiser you need. They only act on water that is moving, so they supplement circulation rather than replacing a residual sanitiser in the tub itself. Both are common options on finished plunges and both need their cells or lamps replaced periodically.
Chemical sanitiser
Most owners still keep a low residual, commonly chlorine or bromine at spa-style levels, tested with strips. Cold water holds sanitiser well and demand is lower than in a hot tub, so quantities are small. Follow the tub maker's guidance rather than a hot tub's: some plunge liners and chiller components do not tolerate every product.
When to just change it
Even a well kept tub accumulates dissolved solids. With filtration, treatment and a cover, monthly changes are typical for regular use; without them, weekly. Signs it is due are cloudiness that will not clear, a film at the waterline or an odour. Changing water is cheap. Sitting in water you are unsure about is how the habit ends.
Questions people ask about cold plunge cleaner
Does cold water need sanitiser?
Yes. Cold slows growth but does not prevent it, and a tub used by people needs filtration and usually a low chemical residual.
Can I use hot tub chemicals?
Often, at lower doses, but check the tub maker's guidance first. Some liners and chiller components do not tolerate every product.
How often should the water be changed?
Monthly is typical with filtration, treatment and a cover. Weekly without them, and immediately if it is cloudy or smells.