Octet Comparator Method For determining aluminum in water Sufficient for 50 tests Octet Comparator has color standards representing 0, 0.1, 0.15, 0.2, 0.25, 0.3, 0.4 and 0.5 ppm. A pink to red color will form when aluminum reacts with Eriochrome Cyanine R, at pH 6.