I just got a new refill of R-0013 from tftestkits I also got the 50 ppm standard so I could make sure I'm doing the test correctly. With the standard I couldn't ever get closer than 55 - and that only with holding it at chest level. The color of the ground makes a big difference too - I have three different color concretes and the lighter grey one got me the closest to 50 at 55 or so.
Ok so I have an error of 5-10 maybe my eyes are going.
So then I test my pool pulling a sample from as low as I could. 2 months ago I measured it at 60 or 80 and my mom and pop pool store that I trust measured it at 60. Today I measured it at 30 or lower??? How could I possibly have lost 30 ppm? Is it possible that the rest reagent is bad? I ordered the big bottle so I could do this test multiple times to calibrate my testing process. It arrived yesterday so it's not like it's been sitting around. Could it have been damaged in travel from excessive heat?
I'm taking a sample to the pool store tomorrow but I'm stumped on this.