Pink Slime in a Pool: What It Is and How to Remove It
Pink slime is a bacterium, not algae: a slick pink or reddish film in skimmers, return fittings, light niches, and on toys, often in spots where chlorine circulates poorly. To remove it, scrub every surface it touches, clean or replace the filter, and raise chlorine only as your product's label directs while the pump runs.
Always follow your product’s label directions. Pool and spa chlorine, bromine, shock and algaecides are EPA-registered pesticides: use products labeled for pool or spa use, and don’t swim or soak until levels are within the limit on your product’s label. If this page and a label disagree, the label wins.
On this page (8 sections)
People call it pink algae or pink mold, but it is usually reported as a bacterium in the genus Methylobacterium. Like other bacteria, it protects itself with a slimy layer called biofilm, and that layer, not the bacterium itself, is what makes it hard to get rid of.
What pink slime is
Pink slime grows as a biofilm: a thin, slippery layer of bacteria held together by the slime they make. Free-floating bacteria are easy for chlorine to kill. Bacteria inside a biofilm are shielded, so chlorine in the water can pass over them without much effect. Orenda, a pool chemical maker, notes that it favors PVC surfaces with little or no sunlight, which is why the inside of skimmers, pipes, and fittings matters so much.
A 1995 study in Applied and Environmental Microbiology found that most Methylobacterium strains taken from chlorinated water systems were chlorine resistant. That fits what pool owners see: it survives in water that tests fine and comes back from the plumbing.
Is it pink slime or something else?
| Check | Pink slime | Something else |
|---|---|---|
| Color | Pink, salmon, or reddish | Rust brown or red-brown that is flat: possibly iron (see pool stains) |
| Texture | Slick, slimy, wipes off with a finger or cloth | Hard, doesn't wipe off: stain or scale |
| Where | Skimmer walls and lid, return fittings, light niches, ladder treads, pool toys, PVC pipe, hot tub jets | Even tint on the whole floor: water color or stain |
| Free chlorine | Often normal; it grows in low-flow spots | — |
| Comes with | Sometimes white, tissue-like clumps (white water mold) in the same places | — |
White water mold, the other common slime, looks like wet tissue paper and lives in the same places. The cleanup below covers both. Other colors are compared on pool algae types.
Cleanup step by step (pool)
- Take out toys, floats, and anything removable, and scrub them separately (see below).
- Scrub every spot you can reach where slime grows: skimmer walls and lid, skimmer basket, return fittings, light niche, steps, ladder treads, and the waterline. Use a brush or a cloth; the goal is to break up the biofilm.
- Test free chlorine (FC), pH, and stabilizer (CYA), and bring pH into range.
- Raise chlorine with a product labeled for shocking pools, at the amount its label gives, scaled to your gallons. Keep the pump running so the treated water moves through the skimmer, pipes, and filter, where the slime lives. Don't exceed the label amount.
- Clean the filter thoroughly. Rinse a cartridge and soak it in a filter cleaner made for pool cartridges, following that product's label, or backwash a sand or diatomaceous earth (DE) filter as its manual says. Replace a cartridge that stays slimy.
- Scrub the same spots again the next day. Retest FC and keep everyone out of the water until it is back at or below the swim limit on your label.
- Check the skimmer and fittings weekly for a month. Pink film that returns means biofilm is still in the plumbing.
If you add an algaecide as a helper, choose one whose label covers your use and dose it by that label; the algaecide calculator scales a label dose. Algaecide supports scrubbing and chlorine but doesn't replace them.
Hot tubs and kiddie pools
Hot tubs. Pink slime in a hot tub usually lives in the pipes and jets, where water sits between uses. The CDC's Legionella guidance for public hot tubs calls for scrubbing all surfaces each time the tub is drained, because biofilm builds inside the system; the same habit helps at home. The usual fix:
- flush the lines with a line cleaner made for hot tubs, following its label, then drain the tub;
- scrub the shell, jets, cover underside, and filter compartment;
- clean or replace the filter, then refill and start fresh.
Step-by-step: how to flush hot tub lines. After a refill, the first-fill steps get the water back in range.
Kiddie and small inflatable pools. Pink film in a small pool usually means the water has been sitting. Drain it, scrub the walls and floor with soapy water, rinse well, and let it dry fully before refilling. For a small pool, a fresh fill is simpler than treating old water. Keeping chlorine in range in small pools is covered on kiddie pool chlorine.
Cleaning toys and gear
- Scrub toys, floats, and noodles with mild dish soap and water. Rinse them well and let them dry fully before they go back in the water. Don't soak them in pool chlorine or bleach.
- Check the hidden spots: the inside of hollow toys, valve caps, the underside of ladder treads, and the feet of removable steps.
- Never mix pool chlorine with household cleaners, and rinse soap off gear before it goes back in the pool.
Keep it from coming back
- Keep FC at or above the minimum for your stabilizer every day. The table is on pool chlorine levels.
- Run the pump long enough each day for water to move through every part of the system, and point return jets so they stir corners and steps.
- Wipe the skimmer, lid, and fittings when you empty the skimmer basket.
- Clean the filter on schedule. A slimy filter is the most common source of repeat growth.
- In a hot tub, follow a regular water-change and line-flush schedule; the water change calculator estimates how often.
The calculator below shows the minimum and target FC for your stabilizer. With its default CYA of 40 ppm, the minimum is 3 ppm and the target is 3–5 ppm. For shocking, it points you to your product's label.
Safety. Always follow the product label. It is a violation of federal law to use a pesticide product in a manner inconsistent with its labeling. Never mix chlorine with household cleaners, line cleaners, other chlorine products, or acid; add each product separately and rinse between them. Wear gloves and eye protection. No swimming or soaking until chlorine is back at or below the limit on your label. Poison Control: 1-800-222-1222.
FAQ
Why does pink slime keep coming back?
It lives in a biofilm inside skimmers, pipes, fittings, and the filter, where chlorine in the water reaches it poorly. If you treat the water but don't scrub those spots and clean the filter, it regrows from what is left.
Is pink slime the same as pink mold?
No. Despite the names, it is usually a bacterium (reported as Methylobacterium), not a mold or algae. The cleanup is the same either way: scrub, clean the filter, and keep chlorine in range.
Can pink slime grow in a hot tub?
Yes. It often grows in hot tub pipes and jets. Flush the lines with a hot tub line cleaner, drain, scrub, clean the filter, and refill.
Sources
- Hiraishi A. and others, Phenotypic and genetic diversity of chlorine-resistant Methylobacterium strains isolated from various environments, Applied and Environmental Microbiology, 1995: pmc.ncbi.nlm.nih.gov
- Orenda, Understanding algae (pink slime and PVC surfaces with little sunlight; white water mold): blog.orendatech.com (a chemical maker's blog)
- Wikipedia, Pink algae (Methylobacterium, biofilm): wikipedia.org (secondary)
- CDC, Controlling Legionella in hot tubs, for public hot tub operators (biofilm, scrub surfaces each time the tub is drained): cdc.gov