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Cloudy hot tub water: causes and fixes
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In short
Cloudy hot tub water usually comes from a dirty filter, low sanitiser, high pH or alkalinity, or hard water. Check the filter first, then test and correct alkalinity, pH and sanitiser, then shock. If it is still cloudy after a day of filtering, or the water is old, a drain, clean and refill is often quicker.
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Cloudy water is the most common water problem in inflatable hot tubs, and it is rarely serious. It means fine particles or dissolved minerals are floating in the water and scattering light. The trick is to work through the causes in order, starting with the simplest, rather than adding several chemicals at once. This guide takes you through filter, balance, sanitiser and hard water checks, explains what to do when the chemicals are balanced but the water is still cloudy and when it is time to drain and refill.
Check 1: the filter
On an inflatable tub, the filter cartridge does most of the work of clearing particles. If it is clogged with oils, scale or debris, water flows through it slowly and particles stay in the tub. Remove it and look: a grey or slimy cartridge, or one that does not rinse clean, needs cleaning or replacing.
Rinse the cartridge with a garden hose, working between the pleats. Soak it in a filter cleaner if the label suggests, then rinse. If it is worn or misshapen, fit a new one. Run the pump for several hours with a clean filter before judging the result. See how to clean hot tub filters.
Check 2: alkalinity and pH
High pH and high alkalinity make minerals drop out of solution, which turns water milky, and they make sanitiser less effective. Test with a fresh strip. If alkalinity is high, bring it down gradually with pH reducer, as the label directs, then correct pH.
Adjust alkalinity first, then pH, waiting the time on each label and retesting in between. Commonly quoted ranges are around 80 to 120 ppm for alkalinity and 7.2 to 7.6 for pH, but use your test kit's ranges.
pH
Target band: 7.2 to 7.6 (scale 6.8 to 8.0)
Total alkalinity
Target band: 80 to 120 ppm (scale 40 to 200 ppm)
Free chlorine or bromine
Target band: as on the product label (scale 0 to 10 ppm)
Common guidance only. Always follow the ranges and safety instructions on your own test strips and chemicals.
Check 3: sanitiser and shock
Low sanitiser lets bacteria and organic waste build up, which clouds the water. If chlorine or bromine reads low, bring it back into range. Then shock the water to break down waste that has built up, following the label for your tub's litres and leaving the cover off for the time stated.
Run the pump with the clean filter afterwards so it can catch the particles the shock has broken down. See how to shock a hot tub.
Check 4: hard water
In hard water areas, which cover much of England, calcium can come out of solution as the water heats, especially when pH is high. This gives a milky look and leaves scale on the liner and heater. Keeping pH in range helps, and an anti-scale product can be used as general guidance, following the chemical maker's instructions. Some tubs, such as several Intex models and the BANGBANGJI tubs, list a built-in hard water treatment system. See hard water and limescale.
Balanced chemicals but still cloudy
If the readings are in range and the water is still cloudy, the likely causes are a filter that is not catching fine particles, high dissolved solids in old water, or lotions and detergent residues from swimwear. Try a new filter, shock and run the pump for a day. A clarifier can help clump fine particles so the filter catches them, used as the label directs.
If that does not work, or the water has been in the tub for many weeks, drain, clean and refill. Fresh water with a clean filter is often the quickest fix of all. See how to drain an inflatable hot tub.
| Cause | Sign | First fix |
|---|---|---|
| Dirty filter | Grey or slimy cartridge | Clean or replace |
| High pH or alkalinity | Test reads high | Lower alkalinity, then pH |
| Low sanitiser | Test reads low | Raise sanitiser, then shock |
| Hard water | Milky look, scale on liner | Keep pH in range, anti-scale |
| Old water | Readings hard to hold | Drain, clean and refill |
Stopping it coming back
Most cloudy water comes back for the same few reasons, so a steady weekly routine prevents it far better than a big fix later.
- Shower before using the tub and avoid lotions.
- Keep the cover on between uses.
- Rinse the filter every few days and replace it when worn.
- Test a few times a week and top up sanitiser after use.
- Shock weekly or after a busy session.
Note:Do not use the tub while the water is very cloudy, as you cannot see the floor. Follow the chemical maker's instructions for every product and keep chemicals away from children.
Frequently asked questions
Why is my hot tub water cloudy after adding chemicals? Adding several products at once, or a high pH, can cloud the water. Run the pump with a clean filter and retest.
Why is my hot tub cloudy when the chemicals are balanced? Often a dirty filter, old water or residues. Clean the filter, shock and run the pump, then drain and refill if needed.
Is cloudy hot tub water safe? Do not use it until it clears and readings are in range.
How long does cloudy water take to clear? With a clean filter and correct balance, often within a day of running the pump.
What you need
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MSpa Tidal: semi-rigid 6 seater, 930 L
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Lay-Z-Spa 60001: 4 seats and 669 L