What causes copper staining on my Ottawa pool's vinyl liner and how do I prevent it?

Copper staining on vinyl liners shows up as blue-green or teal-coloured streaks and patches, and the cause is almost always dissolved copper in the water that precipitates out and bonds to the liner surface. In Ottawa pools, this happens most commonly from two sources: copper-based algaecides added directly to the water, and corrosion of copper plumbing or heat exchanger components caused by low pH or aggressive water chemistry.

Ottawa's municipal water supply from the Ottawa River and groundwater sources in surrounding communities like Kanata, Barrhaven, and Manotick can vary in mineral content and pH depending on the season and your specific neighbourhood. Spring fill water after opening is often slightly acidic, and if you're running a gas heater with a copper heat exchanger — which most older pool heaters have — that acidic water will slowly dissolve copper from the exchanger and carry it into circulation. Over a full Ottawa season, even mildly low pH can leach enough copper to leave visible staining by late August.

Prevention comes down to consistent water chemistry. Keep your pH between 7.4 and 7.6, total alkalinity between 80 and 120 ppm, and calcium hardness between 200 and 400 ppm. These ranges create a balanced, non-corrosive environment that protects both your liner and your equipment. Test your water at least weekly during the Ottawa swimming season — the heat and sun intensity in July and August can shift chemistry faster than you'd expect. Many Ottawa pool supply stores offer free water testing, which is worth doing at the start of the season and again mid-summer.

If you use a copper-based algaecide, never pour it directly into the pool in one spot. Dilute it first and distribute it around the perimeter with the pump running to avoid concentrated copper settling on the liner surface. Better yet, consider switching to a non-metallic algaecide or a salt chlorinator system, which reduces the need for algaecides altogether by maintaining a consistent sanitizer level.

For existing copper staining, a sequestering agent (also called a metal chelator or stain remover) can lift light to moderate staining by binding the copper ions and allowing them to be filtered out. Products like these are available at any Ottawa pool supply retailer. For heavier staining, a professional liner cleaning treatment may be needed — and it's worth having the water tested for total dissolved metals at the same time to address the root cause.

One important caution: never attempt to scrub copper stains aggressively with abrasive pads or brushes. Vinyl liners scratch easily, and a scratched surface is harder to clean and more prone to future staining. Use a soft cloth or a liner-safe stain eraser with the appropriate chemical treatment.

If your staining keeps recurring despite balanced chemistry, it's worth having a pool professional inspect your heater's heat exchanger and any copper fittings in your plumbing — the source of the copper needs to be addressed, not just the symptoms on the liner.