Cloudy hot tub water: causes and how to clear it

Cloudy hot tub water is almost always caused by one of three things: low sanitizer, high pH or alkalinity, or a dirty filter. Test the water, bring pH to 7.2–7.8, shock, and clean the filter. Most tubs clear within 24 hours. If the water is more than 3 to 4 months old, drain and refill.

What causes cloudy water

Cause	How to tell	Fix
Low sanitizer	Chlorine under 1 ppm or bromine under 3 ppm. May smell musty.	Shock with chlorine, then hold sanitizer in range.
High pH or alkalinity	pH above 7.8, alkalinity above 120 ppm	Lower with pH decreaser per the label.
Dirty or worn filter	Filter is gray, greasy, or over 1–2 years old	Rinse, soak in filter cleaner, or replace.
Body oils, lotions, detergent	Cloudy after heavy use, often with foam	Shock. Clean the filter. Shower before soaking.
High calcium hardness	Hardness above 250 ppm, white haze, scale on the shell	Scale control product, or dilute with softer water.
Old water	Water over 3–4 months old that will not respond	Drain and refill.
Biofilm in the plumbing	Sanitizer disappears overnight, flakes from the jets	Line flush, then drain and refill.

How to clear it, step by step

1. Test the water. Write down sanitizer, pH, alkalinity, and hardness. If you are unsure of the colors, see how to read test strips.
2. Fix alkalinity, then pH. Target 80–120 ppm alkalinity and pH 7.2–7.8. Add one product at a time and wait 20 to 30 minutes between them.
3. Clean the filter. Turn off power at the breaker, pull the filter, and hose between every pleat. If it has been a month, do a filter cleaner soak. Full method in how to clean a hot tub filter.
4. Shock the tub. Use chlorine shock per the label, with the jets on and the cover off for at least 20 minutes. See the shock guide.
5. Run the pump. Run a couple of extra filter cycles, or run the jets for 20 minutes a few times through the day, so the water passes through the filter.
6. Rinse the filter again. It has just caught everything the shock knocked loose.
7. Retest the next day. Hold sanitizer in range. Use a clarifier only if a faint haze remains with all readings good.

When to stop treating and drain

Drain and refill if any of these apply:

• The water is more than 3 to 4 months old.
• It is still cloudy 48 hours after balancing, shocking, and cleaning the filter.
• Sanitizer drops to zero overnight with nobody using the tub.
• You see slimy flakes, or the water has a musty or sour smell.

In the last two cases, run a line flush product through the plumbing before you drain. Biofilm hides in the pipes and will cloud the new water within days if you skip this. See how to drain a hot tub.

Types of cloudiness

Milky white

Usually tiny air bubbles or high calcium with high pH. If a glass of the water clears from the bottom up in a minute, it is air. Check that the water level is high enough and the air controls are off. If it stays milky, check pH and hardness.

Dull gray or hazy

Organic waste and low sanitizer. This is the common one. Shock and clean the filter.

Cloudy with a green tint

Early algae, or metals reacting with chlorine. See green hot tub water.

Cloudy with foam

Soaps, lotions, and soft water. Treat the cloudiness as above and rinse swimwear in plain water, not detergent.

How to keep it from coming back

• Test 2 to 3 times a week and keep chlorine at 1–3 ppm or bromine at 3–5 ppm.
• Shock weekly and after any gathering.
• Rinse the filter every 1 to 2 weeks and soak it monthly.
• Replace the filter every 12 to 24 months. Keeping a spare lets you swap while one dries.
• Shower before soaking. It removes most of the lotion, deodorant, and detergent that clouds water.
• Change the water every 3 to 4 months.
• Keep the cover on when the tub is not in use.

Is the filter the problem?

A quick test: with the power off, hold the clean, dry filter up to the light. If the pleats are flattened, torn, or still gray after a chemical soak, it cannot trap fine particles any more. A new cartridge often clears water that no chemical will. Measure the old one before ordering and browse replacement filters by size.