LaMotte SMART 2 - Manual (Page 236)

INTERFERENCES: Sulfides and large amounts of iron interfere. Color and
turbidity may be removed by standardizing the instrument
with the original water sample. Since silica is a component
of glass waste and a common contaminant, it is suggested to
run a reagent blank using silica-free water. The blank value
is subtracted from the sample concentrations.
Silica–LR 2/3 Smart2 TEST PROCEDURES 2.04