I just got to thinking, have we ever discussed if your water should be tested with the pump circulating or not circulating? Does it make any difference? Just curious. Anybody want to jump on board and offer opinions? :?
The only real issue is to not sample near the returns while the pump is running if you have any kind of chlorinator. That assumes you've had enough circulation since the last chemical addition to mix everything.
I take my test samples from near the skimmer in the deep end since my returns are in the shallow end. I also wait about 30 mintues after adding chemicals (if liquid or predissolved) and brush the pool to make sure they are mixed. If I add anything dry I brush until it all seems to be dissolved and then wait about 6 hours to overnight before testing. I wait 24 hours before tesing salt, baking soda (for TA) or borax since it seems to take a while for the chemistry to stabilize after adding them. If the chemicals have mixed I don't think it really matters if the pump is on or off.