Symptoms
- Rough, chalky white or gray band around the pool at the water's surface
- Buildup feels crusty or scratchy to the touch
- Tile or liner discoloration along the waterline
Likely causes
- CommonHigh calcium hardness in the pool waterExcess calcium precipitates out of the water and deposits at the waterline.
- CommonHigh pH causing minerals to come out of solutionElevated pH reduces mineral solubility, encouraging scale formation.
- PossibleEvaporation concentrating minerals at the surfaceAs water evaporates, dissolved minerals become more concentrated right at the waterline.
What to do
- Test water for calcium hardness and pH, and compare to the recommended ranges for your pool type.
- Scrub the scale off with a pumice stone (safe for plaster/concrete) or a non-abrasive scale remover pad (for vinyl or fiberglass) matched to your pool surface.
- Use a scale-specific cleaning product for stubborn buildup, following instructions to avoid damaging the surface or liner.
- Adjust pH down into the recommended range if it's testing high.
- If calcium hardness is very high, consider partially draining and refilling with fresh water to dilute it, especially before adding a scale-preventing product.
- Add a scale inhibitor/sequestering agent to help keep minerals suspended in the water going forward.
Tools and parts
- Pumice stone or scale removal pad (surface-appropriate)
- Pool test kit
Pool scale removerSearch: “pool waterline scale remover”
Scale inhibitor/sequestrantSearch: “pool scale sequestering agent”
When to call a pro
For tile with heavy, long-term scale buildup, a pool tile cleaning service has equipment to safely remove it without damaging grout or tile.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.