Appearance
- Can occur in many different shapes and colours – yellow, green, black, brown etc.
Causes
- Results from decaying organic material (e.g. leaves) settling on the surface.
- Free floating algae bonding with calcium particles which then plate out the surface.
Removal
- Depending on the severity of the stain, raising the free chlorine level (to approximately 5 ppm) may be sufficient to remove the stains.
- If the stain is severe then sprinkle stabilised granular chlorine on the surface and allow to sit until stain has been removed.
- If stain is greater than 30 cm treat as calcium scale (refer to Calcium Scale Fact Sheet).
If chlorine doesn’t remove the stain then the citric acid method should be tested. Citric acid is a very effective oxidiser and works well to break down stains.