You guys are talking about testing your QF. I've called to verify my batch is good - however you mention strips to check for creatine levels. As far as I know, according the to instructions for QF, you aren't supposed to open and close and re-open to use. You can warm up multiple times as long as it hasn't been opened
You must be thinking of a different product. The QF instructions state no such thing.

The QF instructions are found on Spectrum Labs' (the QF manufacturer) website urineluck.com.

Ive tested dozens of QF batches, and repeatedly, for nearly a decade with no problems as a result of opening, closing, and reopening of the bottles.