Start with a water test
Before adding anything, test the water for sanitizer (free chlorine or bromine), pH, and total alkalinity. Most cloudy water is a chemistry problem and the test tells you which one. Adding chemicals blind is how a cloudy spa turns into a foamy, smelly spa.
1. Low sanitizer
The most common cause. When free chlorine or bromine drops to zero, bacteria and organic matter from bathers are no longer being oxidized and the water goes hazy within a day. Bring the sanitizer back into range and shock the spa. If the water clears over the next 24 hours with the circulation running, that was it.
2. pH or alkalinity out of range
High pH (above about 7.8) makes dissolved minerals come out of solution as a fine haze and also makes chlorine much less effective, so you get both problems at once. Low alkalinity lets pH swing around with every use. Balance alkalinity first, then pH, then recheck the sanitizer. The jets in a hot tub drive off carbon dioxide and push pH up over time, so this one creeps back and needs regular attention.
3. A dirty or worn filter
A hot tub filter does a lot of work for its size. When the pleats are coated with body oils and lotion, water bypasses the filter instead of passing through it, and fine particles stay suspended. Rinse the cartridge with a hose every couple of weeks, deep clean it with a filter cleaner every month or two, and replace it once a year or so. A filter that stays flat and grey after cleaning is done.
4. High bather load or body products
A big group, a long soak, or a lot of lotion, sunscreen, hair product, or detergent in swimsuits dumps organic load into a very small body of water. The water goes cloudy and often foams. Shock the spa after heavy use, rinse swimsuits in plain water, and ask guests to shower before getting in. A short circulation cycle with the cover off after a party helps too.
5. The water is spent
If the sanitizer is in range, the pH is balanced, the filter is clean, and the water still clouds up within a day or two, the dissolved solids are too high for the water to be managed any further. This is the one cloudy-water cause that chemicals cannot fix. Hot tub water lasts about 3 to 4 months of regular use before it needs to be replaced.
The fix is a full water change: a plumbing purge to clear the biofilm in the lines, a complete drain, a deep cleaning of the shell, jets, and filter, and a fresh fill with startup chemicals. TrueBlue does this as a Spa Refresh. If you are not sure whether your water is spent or just out of balance, a One-Time Spa Care visit tests and balances it, and we will tell you if it needs a refresh instead.