Green water in the hot tub: algae, metals or weak sanitation

Quick answer: Green hot tub water requires a water test. It’s most often weak sanitation, pH out of range, or metals in the water.

This topic comes from recurring questions from pool and hot tub owners: what to measure first, what to dose, when to filter, and when it no longer makes sense to keep treating the water blindly.

• Low chlorine or bromine.
• pH out of range.
• Metals in the fill water.
• Biofilm in the filter or pipework.
• High temperature and small water volume.

1. Stop bathing.
2. Measure the pH, disinfectant and alkalinity.
3. Clean the filter.
4. Depending on the result, shock-disinfect or use a metal-removal product.
5. If there’s odor or slime, drain the water and clean the pipework.

• Don’t dose chemicals without measuring first.
• Don’t mix different disinfection systems without knowing the instructions.
• Don’t wait until a small problem turns into a major cloudiness issue.

• Measure the water regularly and keep a log of what you do.
• Keep the filtration system and filters clean.
• React promptly after heavy bather load.
• Follow the manufacturer’s instructions for the pool, hot tub and chemicals.

Call a service technician or expert if the problem keeps coming back, the water smells bad, people have issues after bathing, or you’re not sure about the technology and dosing.

Should I adjust pH first, or add disinfectant?

In most common situations, measure and correct the pH first, because disinfection performs worse outside the correct range.

Is generic advice from the internet enough?

Not always. Water volume, filtration type, water source and the chemicals used all matter. Treat an online guide as a checking procedure, not a substitute for measurement.