Problem
Pool Stains: How to Identify and Remove Them
Updated 2026-05-22
Pool stains are not just cosmetic. They tell you something about your water chemistry or your source water. Identifying the stain by color is the fastest path to the right treatment.
Why it happens
Iron stains (orange or brown)
Most often from well water fill or from corroding heater coils when pH stays low. Stains appear on stairs, lights and skimmer edges.
Copper stains (blue green or turquoise)
Algaecides with copper, leaching from heater elements at low pH, or a corroded copper plumbing line.
Manganese stains (purple, black or pink dots)
Less common, source water with manganese plus a chlorine reaction. Often appears as small dots.
Organic stains (green brown blotches)
Decaying leaves, worms or other organic matter left in contact with the pool surface.
How to fix it
Identify by color first
Orange = iron, blue green = copper, purple = manganese, brown blotch = organic.
For metal stains, use ascorbic acid
Vitamin C treatment with a metal sequestrant added afterward to keep metals in suspension.
For organic stains, shock then brush
Cal-Hypo at double dose, brush directly on the stain, repeat if needed.
Prevent
Keep pH 7.2 to 7.6 to prevent metal leaching. Use a sequestrant on every fill. Skim daily.
Get an exact reading first
Scan your test strip with PoolSense and get chemistry + recommended action in seconds.
Get PoolSenseFAQ
Can I just scrub stains off?
Not metal stains. They are chemical, not surface dirt. Scrubbing on plaster can damage the surface.
Will draining and refilling fix the staining?
Only if the source water is the cause. If pH is low and your heater leaches metal, the stains return.
Does PoolSense detect stain causes?
Indirectly. Low pH and visible signals show up in scans. Combine that with stain color to identify cause.