Thanks all. Glad to see it's not just me! I'll probably just continue what I'm doing then- test weekly with the FAS-DPD and occasionally in between with the PS200. I have an Aquarite, so I'm usually just making sure I have a decent Cl and pH reading every couple of days. It seems to stay pretty constant with the Cl, and the pH climbs gradually as expected between the muriatic acid doses.

Thanks,
Steve