Why is my hot tub water cloudy?

Cloudy water is a sign, not a problem of its own. Something in the water is not being sanitized or filtered out, or the water's balance has pushed minerals out of solution. Work through the causes in this order.

1. Sanitizer is low. Test first. Water with too little sanitizer clouds quickly, especially after heavy use.
2. The filter is dirty or worn out. Take it out and look. A filter that is gray, flat or more than a year or two old cannot keep up. See how often to clean it.
3. pH or alkalinity is too high. High readings let minerals fall out of the water as a haze.
4. Hardness is too high. The same thing happens with too much calcium.
5. Lotions, oils and cosmetics. They come in on skin and hair, and build up.
6. The water is old. After a few months, water holds too much to clear. See how often to drain.
7. The tub sat unused. Slimy flakes or a film point to buildup inside the pipes, which needs a line flush before a drain and refill.

What to do

Fix what the test shows, one thing at a time, with your product's own instructions. Clean the filter either way. Let the water circulate and test again before deciding it has not worked.

When to stop and drain

If the water is still cloudy after the sanitizer is back in range and the filter is clean, or the water is already a few months old, a fresh fill is quicker and cheaper than more products.

This is general guidance. Your hot tub's owner's manual comes first, and so do the instructions on your products.

Sources: Hydropool: Cloudy water in a hot tub, causes and solutions; Fluidra: Cloudy water in hot tubs, how to avoid it.