Why is my cold plunge water cloudy?

Cloudy plunge water almost always traces back to one of five causes. Work through them in this order — it runs from most common to least — and fix the first one that sounds like your situation. One thing to know up front: cold water clears more slowly than a hot tub, so give each fix 1–2 hours (sometimes overnight) before deciding it didn't work and trying the next thing.

1. Your sanitizer is depleted

The most common cause. If you haven't dosed in a week, your residual is probably gone, and the haze is biological load starting to win. Test first, then dose to the target range:

2. The filter cartridge is dirty

Gunk in the cartridge both clouds the water directly and quietly drops your circulation. Pull it and rinse under a strong hose for 1–2 minutes. If it hasn't had a deep clean in a month, soak it overnight in a 10:1 water-to-vinegar solution. Cartridges older than ~90 days are usually past saving — replace.

3. Heavy recent use

Multiple people or daily back-to-back sessions add body oils, sweat, and skin faster than the sanitizer burns them off. Run the circulation pump for at least 4 hours to push everything through the filter, and skip a session if you can. This is also the case where an after-session top-up dose matters most.

4. The water is just old

Past a certain age, dissolved solids and biofilm build up and no amount of dosing brings the sparkle back. If you're past your change interval, draining is the fix — not more chemicals:

5. You just shocked or dosed heavily

A heavy dose clouds water briefly on its own. If this is the only box you tick — you shocked recently, sanitizer reads fine, filter is clean, water is fresh — just wait 12–24 hours and re-check before doing anything else.

Related: Cold plunge water testing: strips, targets, and how often · How often should you change cold plunge water?