A big +1 on what "Scut Monkey" said. Checking a sanitizer visually is akin to determining the end of fermentation by looking at the wort. If you like these methods, you'd probably also enjoy Las Vegas.
Pragmatically, I put aside most of a gallon jug of Star San solution last Fall when I quit brewing for Winter. When I checked it in the Spring (yes, Virginia, with pH test strip) it was just peachy-fine, < 3 pH. I might note that I mix Star San only with the RO (reverse osmosis) water from the supermarket, due to the high concentration of calcium and iron in our well water.
“Malt does more than Milton can / To justify God’s ways to man”
-A. E. Housman (1859–1936). A Shropshire Lad , 1896.