the invention includes a composition for stabilizing chlorinated water to sunlight decomposition , and methods of preparing compositions . the composition is a slurry composition of a monoalkali metal cyanurate , of low viscosity . two methods of preparing the slurry are described , in which cyanuric acid or cyanuric acid wetcake is mixed with a monoalkali metal base . one method dry blends cyanuric acid or cyanuric acid wetcake with a monoalkali metal base . the invention also describes a method of preparing a dry , solid monoalkali metal cyanurate .