How to clean a cold plunge

The short version: skim what falls in, keep it covered, dose weekly, check the water before you get in, and drain on a schedule set by what equipment you have. A bare tub with no filter and no ozone needs a full change every one to two weeks. Add filtration and you are into weeks; add ozone or another sanitizer and dosing becomes the routine rather than draining. Nothing here is complicated, and skipping it is what turns a plunge into a chore you stop doing.

What actually grows in cold water

Cold slows biological activity; it does not stop it. What goes into the water is you — skin cells, sweat, oils, whatever was on your feet — plus anything airborne if the tub sits outside. Left alone, that becomes cloudy water, then a slick film on the walls, and the film is the real problem because it hides from a quick rinse. A tub that smells is already past the point where a dose fixes it.

The routine, by equipment

Dosing, and why the labels disagree

The treatments in this category publish genuinely different instructions, and the difference is chemistry rather than marketing. One publishes 1 oz per 100 gallons weekly. Another asks for 16 oz per 100 gallons to start and 2 oz per 100 gallons after that. A hypochlorous-acid product asks for 8 oz a week per 100 gallons. A chlorine- and bromine-free sanitizer asks you to maintain a concentration rather than pour a volume. Those are not interchangeable, and doubling a dose because the water looks cloudy is how people end up with irritated skin and a tub that still looks cloudy. Our best cold plunge water treatments page sets the dosing instructions side by side.

Filtration changes the job

A filter moves the work from your schedule to a cartridge. A 10-inch housing with a 50-micron cartridge catches hair and skin and the visible debris; finer cartridges catch more and clog sooner. What filtration does not do is sanitize — it clarifies. The pairing that actually keeps water usable for weeks is a filter for particles plus a sanitizer for what is dissolved, which is why most chiller manufacturers ship ozone alongside the pump. Our cold plunge filtration guide covers what each stage removes, and best cold plunge filters covers the hardware.

Draining and refilling without wrecking the tub

1. 1Turn the chiller off and let the pump stop before you open anything.
2. 2Drain from the bottom if the tub has a valve; siphon if it does not. Do not tip a full inflatable — a few hundred pounds of water moving at once tears seams.
3. 3Wipe the waterline with a soft cloth and a cleaner made for the job. Household bathroom sprays leave residue that foams next fill.
4. 4Rinse the filter housing and the cartridge, or replace the cartridge if it is discolored and no longer rinses clean.
5. 5Refill and dose before the first session, not after it.
6. 6Log it. A note on your phone beats trying to remember when you last changed 100 gallons of water.

What not to use

• Pool chlorine tablets in a floating dispenser. They are formulated for far larger volumes and warmer water; the concentration in a 100-gallon tub is hard to control.
• Household cleaners inside the tub. Residue foams and irritates skin, and some attack vinyl and drop-stitch coatings.
• Pressure washers on inflatable walls. They drive water into seams.
• Scouring pads on acrylic or PE shells. They scratch, and scratches hold biofilm.
• Guesswork. If the water is cloudy and the dose did not fix it, change the water rather than adding more chemistry.

Cold weather notes

In winter the water stays clean longer and the equipment becomes the fragile part: a filter housing full of water will crack if it freezes, and so will a pump. If the tub lives outside through a freeze, read how to winterize a cold plunge before the first hard night — the cleaning routine changes less than the plumbing routine does.

Every pick on this page comes from published specifications, not from hardware we own. Read how we pick — including what spec-led ranking cannot tell you.