What does residual hardness mean in practice?
A small amount of calcium and magnesium after softening may come from set blending, puncture or internal leakage.
When does it matter?
Permissible level depends on application; a steam boiler and a home installation have different requirements.
Which solutions are related to it?
It is measured by an accurate test at various flows and determines the source before correcting the regeneration or mixing valve.