C-8501 Low Range Phosphate, ortho Comparator is a component of K-8510 Phosphate, ortho CHEMets Visual Test Kit and is designed to be compared against the color formed in R-8510 Phosphate, ortho CHEMets Refill. The comparator's range is applicable to many environmental and water treatment applications. Color standards are blue in color and cover a range of 0 to 1.0 ppm PO₄.