Red, pink or slimy water: what a pink coating in the pool and hot tub means

Quick answer: Treat pink slime or a red coating as biofilm and a hygiene problem: clean mechanically, check the pH, shock-disinfect, clean the filter and, for a hot tub, the pipework too.

Red water is less common than green or brown, but people ask about pink coating, slime in corners, around jets or on steps. It’s often biofilm or a microbial coating, sometimes metal staining.

• Biofilm in pipework, jets or on the walls.
• Low disinfectant level and a long-uncleaned filter.
• Cosmetics, sweat, oils and organic load.
• Metals or sediment from the source water.

1. Stop bathing until the water is hygienically stable.
2. Mechanically clean slimy spots, steps, jets and the waterline.
3. Measure the pH and disinfectant.
4. Perform shock disinfection according to the manufacturer’s instructions.
5. Clean or replace the filter.
6. For a hot tub, use a pipe cleaner and replace the water if the smell is strong.

• Don’t just mask the problem with scented chemicals.
• Don’t touch the slime without washing your hands afterward.
• Don’t leave biofilm in the hot tub’s pipework until the next water change.

• Shower before entering the hot tub.
• Clean the filter regularly, often weekly for a hot tub.
• Keep the pH and disinfectant stable.
• Clean the hot tub’s pipework at every water change.

Call an expert if the slime returns after cleaning, the water smells, or someone develops a rash or health issues after bathing.

Is pink slime an algae?

It’s often called that, but in practice it can be a bacterial biofilm. That’s why a regular dose of algaecide isn’t enough.

Do I have to drain the water?

For a pool, thorough cleaning and filtration is often enough. For a hot tub, with slime, foam and odor, a water change is often worthwhile.