Thanks Richard,

I knew you would have a "Chemists" explanation for the test. I do try to maintain a constant temp for the sample with a water bath. I have to admit that I use a coffee stir stick I scrounged from Mickey Dees --- They work well and have a nice long handle and can be easily cleaned.

As a side note, Reagents are the least of my pool expenses, so I think I would rather be consistent not "cheap" and risk the results of the test. And yes, I agree it's not all that critical.