Cloudy spa water is the most common complaint in hot tub ownership, and the internet’s usual answer — “add clarifier!” — treats the symptom while the cause keeps making more cloud. Cloudiness is fine particles suspended in the water: dead organics, body oils and lotions, scale, or debris too small for your filter to catch. Find where the particles come from and the water clears itself.
Work through these steps in order. Most cloudy water is solved by step 1 or 2.
Step 1: Test the water — sanitizer first
Grab a test strip before you touch anything else. The single most common cause of cloudy spa water is sanitizer that’s been at or near zero for a few days. Hot water is an incubator; without enough chlorine (3–5 ppm) or bromine (4–6 ppm), bacteria and organics multiply and the water turns hazy, then dull, then swampy.
If your sanitizer reads low or zero, this is almost certainly your answer. Shock the water (step 3) rather than just topping up — a normal dose can’t catch up with several days of growth.
Step 2: Check pH and alkalinity
High pH (above 7.8) causes cloudiness two ways: it lets dissolved calcium precipitate out as fine scale particles, and it cripples your sanitizer so organics build up. If pH is high, fix it first — our high pH guide covers exactly what to add. High calcium hardness (above ~250 ppm) amplifies the scale problem, especially if you have hard fill water.
Step 3: Shock the water
Shocking means adding a large oxidizing dose to burn through accumulated organics — sweat, oils, cosmetics, dead bacteria — that regular sanitizer levels can’t keep up with. If the water is cloudy and smells “chlorine-y,” that smell is actually chloramines (used-up chlorine), and it means the water is overdue for a shock, not over-chlorinated.
- Chlorine spas: use dichlor granules, or unstabilized chlorine if your CYA is already at 30 ppm or higher.
- Bromine spas: use MPS (non-chlorine shock) — it also reactivates the bromide bank in your water.
Run the jets with the cover off for at least 20–30 minutes after shocking, then leave the cover off until sanitizer drifts back into range before soaking.
Step 4: Look at the filter
Even with perfect chemistry, a tired filter leaves particles circulating. Pull the cartridge and look at it:
- Dirty: rinse thoroughly with a hose every 1–2 weeks of regular use.
- Oily or waxy film: a rinse won’t cut it — soak overnight in filter cleaner. Body oils and lotions glaze the pleats and water just slides past.
- Flattened pleats, tears, or a year of service: replace it. Cartridges are consumables, not equipment.
Also run the circulation pump longer. Filters only clean the water that passes through them; in cool weather especially, short filtration cycles are a hidden cause of persistent haze.
Step 5: Only now, consider clarifier
Once chemistry is balanced and the filter is clean, a spa water clarifier has a legitimate job: it clumps the remaining ultra-fine particles into flocs big enough for the filter to catch. Used at this stage it clears the last of the haze in a day or two. Used instead of the steps above, it just gums up your filter while the cause keeps producing cloud.
When to give up and drain
Spa water accumulates dissolved gunk that no chemical removes — every dose you add leaves something behind. If the water is old, foams easily, resists every fix above, or your readings bounce around unpredictably, the water itself is worn out. A common rule of thumb: drain every 3–4 months with regular use (divide your gallons by your daily bather count by 3 for a rough day count). Draining and refilling is a two-hour chore that solves problems no amount of chemistry can.
Catch it before it clouds
If you’d rather skip the math, SpaCheckup calculates the exact amount to add based on your readings — and its reminders make sure the “stretch of days where nobody tested” never happens.