As with all testing, lighting is critical to obtain the best possible match. We advise that when testing outdoors, have the Sun hit your back or shoulders. Never face the Sun – doing that will alter your test results as the UV light will interfere. The same holds true for the CYA test. Have your back or shoulders to the Sun and not facing it. Remove sunglasses.
CYA wait time: It takes that amount of time, in that size sample bottle (#9191), for the R-0013 to react and combine with the CYA in the sample to produce the correct cloudiness. The precise-ness of the tests is not as high when compared to other methods; however, remember that with CYA you don’t need to be down to one or two decimal places for an answer. I've never experienced the CYA level increasing like you described.