Acid chrome blue K is a metal indicator. The solution color of the LAMP (Loop-mediated isothermal amplification) reaction with ACBK (Acid chrome blue K) changes from red to blue based on a decrease in the Mg2+ concentration in the reaction solution. CAS No. Room temperature in continental US; may vary elsewhere.Acid Chrome Blue K is a chemical compound used in various applications, including wastewater treatment, as a metal indicator, and as a nutrient solution for plants. It is also known by other names, including 3270-25-5 and 4,5-Dihydroxy-3-[(2-hydroxy-5-sulfophenyl)azo]-2,7-naphthalenedisulfonic acid trisodium salt.