Pool stains: identify and remove every type (Australian 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 Australian pools, including fibreglass and saltwater systems.
Pool stains: identify and remove every type (Australian 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; acid on an organic stain does nothing useful. Australian pools work harder than most — the season runs from roughly October to March in the southern states and close to year-round in Queensland — so there is more sun, more chlorine and more opportunity for a stain to take hold. Identify first, then treat.
| Colour | Likely cause | Quick test |
|---|---|---|
| Green | Iron from bore water or lawn fertiliser | Vitamin C tablet held against the stain (lifts in 30 seconds) |
| Brown / red-brown | Iron or organic (leaves, bark) | Vitamin C test |
| Blue / blue-green | Copper from algaecide or a corroding 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 chemist onto the stain and hold it against the surface for 30 seconds with a brush. If the stain lifts and leaves a lighter patch, it is metal. If nothing happens, it is organic and chlorine will fix it.
This is the single most useful test in stain removal. If you top up from a bore — common in Perth and across plenty of regional areas — assume iron until the test says otherwise.
Removing metal stains
- Drop free chlorine below 1 ppm (mg/L). Strong Australian sun will burn it down in a day or two, or use a chlorine neutraliser (sodium thiosulphate) to speed things up
- Add ascorbic acid at about 12 g per 1,000 litres — roughly 550 g for a typical 45,000-litre 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 as soon as chlorine returns — the stain comes straight back.
Removing organic stains
For organic stains (algae, leaves, pollen), chlorine is the answer. Brush the stain, raise free chlorine to shock level and hold it for 24 hours.
For tough black algae — a real problem in warm Queensland water — scrub with a pumice stone or stainless brush (concrete and pebble pools only), then rest a chlorine tablet 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 fibreglass and vinyl pools
Fibreglass pools are everywhere in Australia, and the gelcoat shows metal stains faster than concrete — though it releases them faster too. Use the ascorbic acid method above, and never touch gelcoat with a pumice stone; it will gouge. Vinyl liner pools are less common here, but the warning applies double: nylon brushes and liner-safe products only.
One more local note: a big share of Australian pools run a saltwater chlorinator. The cell still produces chlorine, so every rule on this page applies — and an ageing copper heat exchanger remains the most common hidden source of blue-green staining.
Prevent stains from coming back
- Add a metal sequestrant at the start of the season, and after every bore-water top-up
- Pre-filter bore water with a hose-end metal filter
- Avoid copper-based algaecides
- Keep pH in range — evaporation and constant top-ups in hot, dry weather push pH and calcium upward, and high pH precipitates metals fast
- Do not abandon the pool over winter (June to August). A quick monthly check and brush stops winter stains before they set in for spring
When to call a pro
Call for a full acid wash (concrete pools only — a nasty job, not DIY). Call for stains that return within a week of treatment: there is a metal source you have not found, often a corroding heater or unfiltered bore top-ups. Most local pool shops will also test a water sample if you want a second opinion on metals.
Stains cost bookings if you hire out your pool
Pool hire is a natural fit for Australia — the season is long, backyards have pools, and guests choose with their eyes. A bright, stain-free pool wins bookings in Sydney, Melbourne and beyond, while a stained one gets scrolled past. If you have been thinking about earning from yours, start with our guide to renting out your pool in Australia.
On money, plainly: prices on Pool Rental Near Me currently display in US dollars, and hosts are paid out in Australian dollars via Stripe. Founding hosts keep 100% of their price — 0% host fees, forever.
Summer here means December to February, and that is when demand peaks. List your pool now and be live before the hot weather hits.
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.