Cloudy Hot Tub Water: Causes and Fixes

The quick answer: test sanitizer, pH and alkalinity, then clean the filter. Most cloudy hot tubs come from:

• sanitizer that's too low;
• high pH or alkalinity, which can make calcium come out of solution as a haze;
• a dirty filter.

If all of those check out, the water is probably old (high dissolved solids) or there's biofilm in the lines, and a flush plus a drain-and-refill is the real fix. Enter your readings below for what to add first.

Work through it in this order

1. Sanitizer: is there enough?

• Chlorine 3–5 ppm, or bromine 4–6 ppm. CDC guidance is at least 3 ppm chlorine or 4 ppm bromine.
• Low or zero? Bacteria and contaminants are multiplying faster than they're destroyed, and that shows up as haze. Shock, then bring sanitizer back into range:
  • Chlorine users: chlorine shock or a large chlorine dose.
  • Bromine users: MPS to regenerate bromine from the bromide bank.
• Chlorine users: a strong "chlorine smell" with cloudiness usually means combined chlorine (chloramines). Shock to clear it.

2. pH and alkalinity: is the water scaling?

Hot water holds less calcium carbonate than cool water. When pH and alkalinity are high, calcium comes out of solution as a fine white haze and as scale on the shell and heater.

• pH above about 7.8, or alkalinity well above about 80–100 ppm, with moderate to high calcium, points to this.
• Fix:
  1. Lower alkalinity and pH with pH decreaser (sodium bisulfate), in steps.
  2. Then let the jets aerate.
  3. See hot tub pH too high.
• Calcium-based products can trigger it in hard-water areas. Cal-hypo shock, some "all-in-one" products and calcium increaser are examples.

3. Filter: is it clogged?

Hot tub filters work hard in a small volume of water.

• Rinse the cartridge every week or two with a hose, pleat by pleat, not with a pressure washer.
• Chemically clean it about monthly with heavy use. Lotions and oils glue the pleats shut, and a rinse won't remove them.
• Replace it when the pleats are frayed or it won't come clean. Many owners rotate two cartridges.
• Inflatables: small filters clog fast. Rinse them often, and replace them when a rinse doesn't restore flow.
• Run the filtration long enough. If your tub runs short cycles, extend them until the water clears.

4. Water age: is it time to drain?

Even with perfect readings, water eventually fills with dissolved solids: body oils, cosmetics, detergents and chemical by-products. It goes dull, foams, and eats sanitizer.

• Use the formula (gallons ÷ 3) ÷ bathers per day to see if you're overdue. See how often to drain a hot tub.
• If you're close to or past it, a refill fixes cloudiness more cheaply than chemicals will.

5. Biofilm: is it coming from the pipes?

If the water clouds up again soon after a shock, if flakes or "snot" come out of the jets, or if it's cloudy right after a refill, biofilm in the plumbing may be releasing debris and eating sanitizer.

• Fix: before your next drain, run a line flush (pipe cleaner) product per the label, then drain, clean and refill.

Special cases

Cloudy after shocking. Some haze is normal for a few hours. Shock oxidizes waste, and the filter has to catch what's left.

• Run the jets with the cover open.
• Check the filter.
• If it's still cloudy the next day, check pH and alkalinity. A calcium-based shock in hard water often causes a calcium haze.

Cloudy after refilling. Look at the fill water:

• Hard water (high calcium and alkalinity): lower alkalinity and pH.
• Well water: metals can cloud or tint the water when chlorine is added. Use a metal sequestrant, or a pre-filter on the hose.
• Biofilm: if you didn't flush the lines before draining, old biofilm may have seeded the new water.

Cloudy only when the jets are on. That's usually air (tiny bubbles) or a suction leak pulling air into the pump. If the water is clear with the jets off, check the water level (too low pulls air) and the filter lid seal.

Cloudy and smelly. That's low sanitizer plus organic load, or old water. Shock, then plan a drain if it returns quickly. See hot tub foam if it's also foaming.

Quick diagnostic table

Prevent it

• Test before each soak, and dose after soaks. Soak when free chlorine is 3 to 5 ppm and at least 7.5% of your CYA (bromine 4 to 6) and pH is 7.2 to 7.8, at least 15 minutes after adding anything (20 after pH decreaser); after chlorine, bromine or a shock, test again first. Above 5 ppm chlorine or 6 ppm bromine, wait and retest in an hour or two; never soak above 10 ppm chlorine or 8 ppm bromine, or with pH below 7.0 or above 7.8. Below 3 ppm chlorine (4 bromine), add sanitizer first; at pH 7.0 to 7.2, raise pH first; with CYA above 40 ppm, drain and refill. Hot tub limits based on CDC guidance and EPA product labels.
• Keep pH about 7.4–7.6 and alkalinity in range.
• Rinse the filter weekly and deep-clean it monthly.
• Shower before soaking, and rinse swimsuits without detergent.
• Drain on schedule, and flush the lines before draining.

Test-before-soak in Spa Calc

Open Spa Calc, tap in your readings, and see whether they're in the soak range: soak, wait, or add this first. The app shows the dose for your products and reminds you about filter rinses and drain day. If cloudiness keeps coming back, your log shows whether it follows high pH, low sanitizer or old water.

One hot tub? Every feature, free. No account, no ads, and iCloud backup is included.

Safety

• Keep chemicals out of reach of children and pets, and keep them out of the water until it is back in range.
• Never mix chemicals. Never add acid and chlorine together: mixing them releases toxic chlorine gas.
• Add chemicals to water, never water to chemicals.
• Store chemicals sealed, cool and dry, apart from each other.
• Read and follow the product label. It always comes first.