In practical terms, there isn’t much difference between scale and encrustation — service technicians use both terms to refer to calcium-based buildup on pool surfaces and equipment.

But at the microscopic level, some distinctions explain why scientists regard these as two separate phenomena.

“Scale and encrustation both occur when mineral or metal compounds precipitate out of water,” says Jim Schmitt, owner of Schmitt Technical Services in Madison, Wis.

In other words, both are the result of water being saturated with more calcium than it can chemically “hold,” and “throwing” out the excess onto nearby surfaces.

The differences become clearer, however, when these deposits are examined under a microscope. “An encrustation will occur as layers of coarse calcite crystals,” Schmitt says, “whereas precipitate — that is, scale — will be finer, and could be multiple layers, almost like a very fine layer cake.”

When it comes to chemical treatments, though, the chemical composition of the scale or encrustation is far more important than its texture.

“Calcium carbonate would respond to a different chemical treatment than, say, a sulfate salt,” Schmitt explains. Even so, abrasive methods like sanding or brushing work largely the same, regardless of a deposit’s chemical composition.