I'm curious. Is there shelf life for the various chemicals we use for testing our pools? I have a 2oz bottle of the R-0871 I ordered from TFTestkits. I think I am in my second season using it. I have lost confidence in the results reported on the chorine tests. I have run these tests often enough & long enough that I can eyeball the range between .5-2 ppm of chlorine. But when I add R-0871 to the mixture created with R-0870, the ppm results reported are generally double expectation. Same is true, of course, after adding chlorine amount recommended by PoolCalculator.
I store my test kit indoors, with the exceptional overnight error.