Why Is My Hot Tub Water Green?
Green hot tub water usually means low sanitizer (algae) or dissolved metals. Here's how to tell them apart and clear it up.
Updated June 2026
Quick answer
Green hot tub water is usually one of two things: low sanitizer letting algae grow, or dissolved metals (often copper) reacting in the water. If it's slimy and grew as your sanitizer dropped, treat it as algae — balance, shock, and filter. If it greened right after adding chemicals and the water's clear, it's metals — use a sequestrant.
Algae or metals?
- Algae — water turned green as sanitizer fell, looks cloudy-green, surfaces feel slick. Adding sanitizer and shocking helps.
- Metals — water greened right after adding chlorine/shock or on a fresh fill, often clear rather than slimy. Copper (from corrosive low-pH water, heaters, or well water) is reacting; more shock makes staining worse, not better.
How to clear it
- 1
Test and balance
Check sanitizer and pH. Low or zero sanitizer points to algae; recently corrosive (low pH) water points to metals.
- 2
If algae: shock and filter
Balance pH, shock the tub, run the jets with the cover off, and clean the filter as it loads up.
- 3
If metals: add a sequestrant
A metal sequestrant binds the copper or iron so it stops tinting the water and the filter can remove it — don't keep shocking.
- 4
When in doubt, refresh
If the water is old or won't clear, a drain and refill with balanced first-fill chemistry is the fastest reset.
True algae is uncommon in a properly sanitized hot tub — green usually means the sanitizer ran out or metals got in. Aquavail helps you keep sanitizer in range so it doesn't start, and flags corrosive water that mobilizes metals.
Common questions
Is it safe to use a green hot tub?
No — wait until it's cleared and sanitizer is restored. Green from algae means the sanitizer is depleted and the water isn't safe; green from metals means the chemistry is off. Fix the cause and confirm a normal sanitizer reading before soaking.
Why did my hot tub turn green after shocking?
That's the signature of metals, not algae — the shock oxidized dissolved copper or iron and tinted the water. Stop shocking and add a metal sequestrant; continuing to shock can cause staining.
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