Cold plunge filter and water care guide

What keeps cold plunge water clean

A cold plunge filter is a cartridge the pump pushes water through to trap hair, skin and grit. It is one of four jobs, and owners on the r/coldplunge forum who keep the same water for months do all four.

The shower comes up more than any product. A technician who maintains cold plunges for a living calls it “the single most impactful thing you can do”, because skin oil, sweat and sunscreen are what bacteria feed on.

We have not tested any of this. The chlorine and pH figures are the CDC’s, the ozone warning is the EPA’s, the filter sizes are makers’ specs, and the routines are owners’ own.

Which cold plunge filter to buy

Buy by micron rating, the size of particle the cartridge stops. Owners have tried the range.

Makers land in the same place. The Pod Company, AS ColdPlunge and 1stplunge all state a 20-micron filter for their chillers, and TURBRO states a 40 and a 20 micron pair.

Two more things from owners. Pleated cartridges hold up, and string-wound ones “start to fall apart” after a few weeks in cold water. And a cartridge filter needs a housing: the builds in our DIY cold plunge chiller guide use a whole-house filter housing from a hardware store.

A chiller with a built-in filter needs none of this. Its maker sells the cartridges, and our best cold plunge chillers says which type each one takes.

How to change the filter on a cold plunge

How often is where owners differ, and it tracks how dirty the water gets.

• Rinse every one to two weeks. Several owners do this and stretch a cartridge to a month or more.
• Replace every one to three months. A technician’s range is three to six months with monthly rinsing.
• Replace sooner if the flow drops. A blocked filter is also the first thing to check when a chiller stops cooling.

The cartridges are cheap. The Pod Company sells a four-pack for $39 and TURBRO a five-pack for $39.99, on their own sites.

Ozone, peroxide or chlorine?

A sanitiser is what kills bacteria, and there is no agreed answer among owners. Here is what each one is and what is known about it.

The CDC gives figures for home pools and hot tubs: a pH of 7.0 to 7.8, and chlorine of at least 1 part per million in a pool and 3 in a hot tub. It adds that chlorine kills germs less well as pH rises, “especially if pH is >8.0”. The CDC has no page for cold plunges, and we found no equivalent public health figure for peroxide or ozone on their own.

That gap matters for one reason. Clear water is not the same as clean water. An owner whose water has stayed clear for months on peroxide and ozone may be right that it is fine, and has no number to check it against. If you want one, chlorine and a test strip give you the CDC’s.

One owner’s experience cuts the other way. After months of bottled treatments and peroxide, with water turning foggy inside a week, they stopped adding anything and ran a 5-micron filter around the clock. The water then stayed clear for weeks. More product is not always the fix.

Ozone generator for a cold plunge

An ozone generator makes ozone gas and feeds it into the water. Owners describe it as a strong oxidiser. Owners like it because it runs on a timer and needs nothing bought or poured.

How owners set it up:

• On a timer. Runs of 30 minutes, an hour, 90 minutes and three hours a day all appear in the threads, usually at night.
• Through a Venturi injector, which draws the gas into the water line, with a one-way valve so water cannot run back into the generator.
• On the return, after the chiller. The order is in our DIY cold plunge chiller guide.

Two cautions from single commenters. One says ozone can corrode a galvanised stock tank and degrade rubber parts. Another notes that it turns clear vinyl tubing cloudy.

How often to change the water

The best advice in the threads is to “change on the test strip, not the calendar”. If the water tests in range and stays clear, there is no reason to dump it. Change it when it turns cloudy, smells, or will not come back into range.

Fresh water costs ice. Every refill starts warm again, which is one more reason regular plungers move to a chiller. The sums are in how much ice an ice bath needs.

How to clean a cold plunge tub

The slippery film on the walls is biofilm, and owners say it forms even in water that looks clean.

• Wipe the walls weekly with a microfibre cloth. One owner puts a little 3% hydrogen peroxide on it.
• Scrub when you drain. A non-abrasive pad, the white kind, so you do not scratch the surface.
• Do the lid seal and the corners. One owner points out that the gasket and the spots the pump does not reach are where biofilm hides.
• Rinse the filter while the tub is empty.

A portable ice bath with no pump gets the same treatment more often. Owners of soft pods shower first, keep the lid on and change the water every two to three weeks. Some makers sell a kit for this: Ice Barrel lists one with cleaning soap, a stabiliser, a brush and a net.

What you need

A filter housing and cartridges if your chiller has no filter, a sanitiser, and test strips that read whatever you use: chlorine and pH strips for chlorine, peroxide strips for peroxide. Both kinds are in the list beside this page. A chiller with the filter built in covers the first of those, and our picks are in the best cold plunge chillers.

Common questions