CYA disappears over the winter

[chem geek]

FYI to those interested in obscure questions and answers. I had seen on several websites that the manufacturers of melamine cyanurate claim it has a solubility of 0.002g/100ml which would work out to 20 ppm. The Taylor K-1720 kit measures CYA down to 20 ppm so I thought "how is this possible?" and wrote to Taylor to find out. After all, if CYA were soluble at 20 ppm, how could you the black dot get obscured so you could get a 20 ppm measurement?

Taylor is a great company who answer any ridiculous question I ask (apparently) and they came back with the response that the standard solubility measurements are done in distilled water so they start out at a pH of 7. The CYA reagent used in the CYA test (which contains melamine) is buffered at a low (acidic) pH and apparently the solubility of the melamine cyanurate complex is less soluble at low pH and is essentially insoluble at the pH of the test so they can measure rather low levels of CYA in the test.

Richard