Compositions, apparatus, and methods for determining hardness of water and magnesium ion in an analyte composition

A method of determining the hardness and/or magnesium ion concentration of an analyte composition, the method comprising:

• a) obtaining a hardness and/or magnesium assay kit comprising:
• (i) a microwell plate;
• and
• (ii) a lyophilized composition comprising an indicator, a buffer, and one or more excipients,
• wherein a plurality of microwells of the microwell plate contain the lyophilized composition such that when an analyte composition is added to the lyophilized composition in each microwell of the plurality of microwells a solution forms having an absorbance at a detectable wavelength in response to the hardness and/or magnesium ion comprised in the analyte composition;
• b) obtaining an analyte composition;
• c) adding substantially the same volume of the analyte composition to each of the plurality of microwells of the microwell plate to form solutions from the analyte composition and the lyophilized titrate compositions in each of the plurality of microwells;
• d) measuring the absorbance value for each solution in each of the plurality of microwells at a wavelength and determining the hardness and/or magnesium ion concentration of the analyte composition based on the measured absorbance values,
• wherein the analyte composition is obtained from a drilling process, a fracking process, or a wastewater tank or reservoir or
• wherein the analyte composition comprises a plurality of solutions having the same analyte, and each analyte composition is obtained from a different well of a plurality of subsurface wells.