Guides / TubTender
Cloudy hot tub water: why it happens and how to fix it
Cloudy hot tub water almost always comes from low sanitizer, pH or alkalinity that has crept too high, or a clogged filter, and old water full of dissolved solids makes all three worse. Test the water first, bring alkalinity and then pH into range, shock to restore the sanitizer, rinse the filter, and run the jets with the cover open; most haze clears within a day.
Step 1: test before you add anything
Guessing is how a cloudy tub turns into a cloudy tub with too much acid in it. Dip a fresh test strip, or use a drop kit, and write down four numbers: sanitizer (free chlorine or bromine), pH, total alkalinity and, if your strip has it, calcium hardness.
The free hot tub chemical calculator takes those readings, your tub size and the strength printed on your own bottles, and lists what to add in the right order.
What the readings tell you
Compare your numbers with the usual hot tub ranges. These follow CDC hot tub guidance for soaking and the common spa targets for balance.
| Reading | Usual range | If it is outside the range |
|---|---|---|
| Free chlorine | 3 to 10 ppm | Low chlorine lets bacteria and body oils cloud the water |
| Bromine | 4 to 8 ppm | Low bromine does the same; shocking reactivates spent bromide |
| pH | 7.2 to 7.8 | High pH makes sanitizer weaker and lets calcium come out as haze |
| Total alkalinity | 80 to 120 ppm | High alkalinity pushes pH up and keeps it there |
| Calcium hardness | 150 to 400 ppm | Very high calcium plus high pH turns the water milky and leaves scale |
If every number is in range and the water is still cloudy, the filter or old water is the likely cause.
Step 2: fix it in this order
- Alkalinity first. It buffers pH, so correcting pH before alkalinity means doing it twice. Raise it with an alkalinity increaser or lower it with pH decreaser, following the label on your product.
- Then pH. Bring it to about 7.4 to 7.6 with pH increaser or decreaser.
- Then shock. A non chlorine or chlorine shock (whichever matches your sanitizer, per its label) burns off oils and restores the sanitizer level.
- Rinse the filter with a garden hose, pleat by pleat, from top to bottom. Soak it in a filter cleaner if it is greasy.
- Run the jets with the cover open for about 20 minutes after each addition, wait before adding the next product, and test again before anyone soaks.
Still cloudy the next day?
- Add a spa clarifier. It clumps fine particles so the filter can catch them. Follow its label and rinse the filter a day later.
- Check the filter's age. Most spa filters need replacing about once a year, or sooner in a busy tub.
- Think about the water's age. Most hot tubs need draining and refilling every three to four months. Water near its drain date is often faster to replace than to fix.
- Look at what goes in with the bathers. Lotion, makeup, hair products and detergent in swimsuits all cloud water. A quick rinse before soaking helps.
Cloudy or foamy?
Cloudy water is hazy all the way through and usually means a chemistry or filtration problem. Foam sits on the surface and is usually soap, lotion or hair product, often with soft water (low calcium).
Foam often follows the same fix: test, balance, shock and rinse the filter. A spa defoamer knocks it down for the moment, but it comes back until the cause is gone.
A faster way next time
TubTender is an iPhone app from Graysmith Labs that turns a test strip into a plan: tap the colors on your strip, scan the labels of the chemicals you own, and it lists how much of each to add for your tub size, in this same order, with a countdown until the water is safe to soak. Its cloudy and foamy water guides are free.
TubTender 1.0 is in App Review. Until it is live, the free hot tub calculator on this site runs the same engine in your browser.
Questions
Why is my hot tub water cloudy?
Usually low sanitizer, high pH or alkalinity, or a clogged filter. Old water with a lot of dissolved solids makes all of these worse.
Is it safe to use a cloudy hot tub?
It is best to wait. Cloudy water often means the sanitizer is too low to keep the water safe. Test, fix the sanitizer and pH, and soak once the readings are back in range.
How long does it take to clear cloudy hot tub water?
Most haze clears within 24 hours once the water is balanced, shocked and the filter is clean. If it is still cloudy after that, try a clarifier or drain and refill.
Will shock clear a cloudy hot tub?
Often, if low sanitizer or oils are the cause. Balance alkalinity and pH first so the shock works, and rinse the filter so it can catch what the shock breaks down.
Should I drain a cloudy hot tub?
Drain and refill if the water is near its drain date (typically three to four months), if calcium or dissolved solids are very high, or if balancing and shocking have not cleared it.