← Moon Dog · Cold Plunge Guides
How often should you change cold plunge water?
The honest answer: it depends on two things — whether your plunge has a chiller and filter, and which sanitizer you run. A chiller-and-filter plunge on chlorine can go a month between changes. A DIY chest-freezer plunge on peroxide needs fresh water weekly. Here's the breakdown.
Water-change cadence
| Setup | Sanitizer | Change water every |
|---|---|---|
| Chiller + filter | Chlorine | 28 days |
| Chiller + filter | Hydrogen peroxide | 14 days |
| DIY / no chiller | Chlorine | 14 days |
| DIY / no chiller | Hydrogen peroxide | 7 days |
Two factors drive the spread:
- Filtration. A continuously running filter pulls out body oils, skin, and debris between sessions. A DIY chest-freezer build with no circulation relies entirely on the sanitizer residual, so the water fouls faster.
- Sanitizer longevity. Chlorine holds a residual longer than hydrogen peroxide, which degrades comparatively quickly — especially in a plunge that isn't refrigerated continuously.
Heavy use (multiple people, daily sessions) shortens every interval. If the water looks hazy, smells off, or won't hold a sanitizer reading, change it early regardless of the calendar.
Filter cleaning cadence
If your plunge has a filter cartridge, it needs its own schedule — independent of water changes:
| Task | How often |
|---|---|
| Rinse the cartridge | Every 7 days |
| Deep clean (vinegar or cartridge cleaner) | Every 30 days |
| Replace the cartridge | Every 90 days |
Most owners underestimate how fast a cartridge degrades. A clogged filter quietly drops your circulation and shortens how long the water stays clean — which is why a simple reminder beats relying on memory.
Frost tracks all of this for you
Tell Frost your tub type and sanitizer once, and it sets your water-change and filter cadence automatically — then reminds you when each is due. It also does your exact dosing math and includes a "water looking off?" diagnostic. No subscription, no ads, works offline.
Sources
- Plunge — water care and filter guidance
- Icebound Essentials — Cold Plunge Water Maintenance Guide
- Sun Home Saunas — Cold Plunge Filtration: Ozone vs UV vs Salt Water
- Morozko Forge — cold plunge guidance
This article is general guidance. Always confirm with your own water testing and your equipment manufacturer's instructions.