Pool stains: identify and remove every type (Canada guide)
By Derek Bowen, founder of Pool Rental Near Me and author of 7 books on pool hosting
Identify a pool stain by its colour, then remove it with the right treatment — ascorbic acid for metals, chlorine for organics. Written for Canadian pools, including well water and vinyl liners.
Pool stains: identify and remove every type (Canada guide)
Identify before you treat
Touching the wrong chemical to the wrong stain can set it permanently. Chlorine on a metal stain locks it in for good; acid on an organic stain wastes your money. Canadian pools carry an extra risk: the season is short — roughly Victoria Day to Labour Day in most provinces — and a stain you find at spring opening has spent months setting under the winter cover. Identify first, then treat.
| Colour | Likely cause | Quick test |
|---|---|---|
| Green | Iron from well water or fertilizer | Vitamin C tablet held against the stain (lifts in 30 seconds) |
| Brown / red-brown | Iron or organic (leaves, worms after rain) | Vitamin C test |
| Blue / blue-green | Copper from algaecide or heater | Vitamin C |
| Black | Black algae OR manganese | Brush hard. If it lifts, algae. If not, metal |
| Pink | Pink slime bacteria | Lifts with chlorine |
| Yellow | Mustard algae or pollen | Brush, then chlorine |
The vitamin C test
Drop a 500 mg vitamin C tablet from the pharmacy onto the stain and hold it there for 30 seconds with a brush. If the stain lifts and leaves a lighter spot under the tablet, it is metal. If nothing happens, it is organic and chlorine will fix it.
This is the single most useful test in stain removal, and it matters even more here: plenty of rural Canadian pools fill from iron-rich well water, so metal staining should be your default suspect.
Removing metal stains
- Drop free chlorine below 1 ppm (mg/L) — let the sun burn it off or use a chlorine neutralizer (sodium thiosulphate)
- Add ascorbic acid at about 12 g per 1,000 litres — roughly 450 g for a 38,000-litre (10,000 US gallon) pool
- Brush the stains. They lift in minutes
- Add a metal sequestrant (HEDP-based) per the label to hold the dissolved iron in solution
- Run the pump 24 hours
- Bring chlorine back to 3 ppm slowly over 3 to 4 days
Skip the sequestrant and the metal redeposits the moment chlorine rises — the stain comes right back.
Removing organic stains
For organic stains (algae, leaves, pollen), chlorine is the answer. Brush the stain, raise free chlorine to shock level, hold for 24 hours.
For tough black algae, scrub with a pumice stone or stainless brush — concrete and plaster pools only — then rest a chlorine puck directly on the spot for an hour.
Pink slime
Pink slime is a bacterial biofilm that resists normal chlorine. Treatment:
- Clean the filter completely (it lives there too)
- Shock to 30 ppm chlorine
- Hold shock for 24 to 48 hours
- Scrub all surfaces
- Run the pump continuously
Stains in vinyl liner pools
This section matters more in Canada than almost anywhere: a huge share of Canadian inground pools are vinyl-lined, because liners cope with freeze-thaw winters. Pumice stones, stainless brushes and acid washing will ruin a liner. Nylon brushes and liner-safe products only. Ascorbic acid is liner-safe for metal stains; never let a chlorine puck rest on the liner. For deep stains in an old liner, sometimes the honest fix is a new liner.
Prevent stains from coming back
- Add a metal sequestrant at spring opening, and again whenever you top up with well water
- Pre-filter well water with a hose-end metal filter every time you add water
- Avoid copper-based algaecides
- Keep pH in range — high pH precipitates metals fast
- Close the pool with balanced water in the fall. Stains set hardest under a winter cover, and an early, clean spring opening is the cheapest stain prevention there is
- Watch for heater corrosion — a leaking heat exchanger dumps copper
When to call a pro
Call for a full acid wash (concrete pools only — nasty job, not a DIY project). Call for stains that return within a week of treatment: you have a metal source you have not found. And call before attacking a vinyl liner with anything aggressive.
Stains cost bookings if you rent out your pool
Canada's swim season is short, which means demand packs into it — every stained weekend is a weekend you cannot get back. Guests browsing pools in Toronto or Vancouver choose with their eyes, and a bright pool wins. For context from the US market, top backyard pools in Southern California earn US$800 to $1,000 in a good summer week; Canadian numbers will differ, but the pattern holds — clean pools book. Start with our guide to renting out your pool in Canada.
On money, plainly: prices on Pool Rental Near Me currently display in US dollars, and hosts are paid out in Canadian dollars via Stripe. Founding hosts keep 100% of their price — 0% host fees, forever.
Ready? List your pool and be bookable before the next long weekend.
Frequently asked questions
- What is Pool Rental Near Me?
- Pool Rental Near Me is a peer-to-peer marketplace where homeowners rent out their backyard pools by the hour. Guests get a private pool, hosts earn money, and every booking requires a signed guest waiver. Hosts carry their own insurance.
- How much does a private pool rental cost?
- Most pool rentals range from $40 to $150 per hour depending on the pool, amenities, location, and time of day. You see the full price before you book.
- How much can I earn renting out my pool?
- That depends on your hourly rate, amenities, and how many hours you host — there is no typical figure we can stand behind. Pool Rental Near Me charges 0% host fees, so you keep 100% of your listed price.