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
“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.