The chlorinated cyanurates (e.g. Trichlor and Dichlor) first made their appearance in sanitizing compounds in 1958 and the use of cyanuric acid in pools was also introduced at that time. These products didn't become more widespread for use in pools until the early 1960's and prior to that time people mostly used chlorinating liquid (or bleach) in residential pools or chlorine gas in commercial/public pools (today, chlorine gas is not used very much).