Hot Tub Problems and Fixes
Almost every hot tub problem starts the same way: test first. The reading usually points straight at the cause, and the fix for one cause can make another worse. Here are the common ones and what they usually mean.
Troubleshooting basics
Fresh test strips come first for every problem below; a metal sequestrant and a hose pre-filter help with green water from metals.
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Quick reference
| Problem | Most likely cause | Where to start |
|---|---|---|
| Cloudy water | Low sanitizer, high pH or a dirty filter | Test, clean the filter, rebalance, shock |
| Green right after chlorine | Metals (usually copper), not algae | Fix pH, metal sequestrant, filter |
| Foam | Lotions, oils, detergent in swimsuits | Shower first; old water needs a change |
| Strong chlorine smell | Used-up chlorine (chloramines) | Shock, then retest |
| pH won't hold | Alkalinity out of range | Fix alkalinity first |
| Scale on surfaces | High calcium or high pH | Lower pH; check hardness |
Green water right after adding chlorine
This one surprises people: green right after chlorine or shock — especially on a fresh fill — is usually oxidized metal, most often copper, not algae. The metal was dissolved and invisible; the chlorine turned it into a colored form.
| Clue | Points to metals | Points to algae |
|---|---|---|
| When it turned green | Right after chlorine, often a fresh fill | Gradually over days |
| Clarity | Clear, just tinted | Cloudy or murky |
| Surfaces | Smooth; maybe blue-green stains | Slimy walls and waterline |
| Sanitizer | Normal or high | Low or zero |
Where the copper comes from
- Fill water, especially well water.
- A corroding heater — the big one if the green keeps coming back. Low pH slowly dissolves copper parts every time the water heats.
- Some copper-based algaecides.
What people usually do
- Bring pH back into range (about 7.2–7.8) so metal stops dissolving.
- Use a metal sequestrant (sold as "stain & scale" or "metal remover") made for spas, following its label.
- Run and clean the filter, where the bound metal ends up.
- Partial or full drain if the metal load is heavy.
- Next fill: a garden-hose pre-filter, especially on well water.
If it is cloudy, slimy and the sanitizer had been low, treat it as algae instead: balance pH, shock, brush the surfaces and clean the filter.
Cloudy water
Test first. Low sanitizer, high pH and a clogged filter are the usual causes, often together. Clean the filter, bring alkalinity and pH into range, then shock. If water stays hazy with good numbers and a clean filter, it is probably old water — see when to change your water.
Strong chlorine smell
A harsh chlorine smell usually means used-up chlorine (chloramines), not too much of it. A shock breaks them down. Leave the cover open while it clears and test before you get in: how long to wait after shocking.
Foam
Body oils, lotions, hair products and detergent left in swimsuits. Shower before soaking and rinse swimsuits in plain water. Defoamer is a short-term patch; foam that keeps coming back means the water is due for a change.
pH that won't stay put, and scale
pH that keeps bouncing almost always means alkalinity is out of range — fix that first (see water balance). Crusty scale on the shell or jets points to high calcium hardness or high pH.
Catch it early
Most of these start as a drift in the numbers days before you see it in the water. HTReminder reads your strip from a photo and keeps your history, so a pH sliding low (the usual trigger for green water) is easy to spot. What you add is always your choice.
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