To be honest: I tested my water just a couple of times since I got my p's, almost a year ago. I never lost a single fish to bad water quality or spikes (*knock on wood*) as of yet: all I do is observing how my fish act, and respond after water changes, equipment changes, or when I've cleaned my filter (to be honest, I'm all over them almost all the time, so I know exactly how they are).
But I must add that we have very high quality tap water over here (well, it's very suitable to use in tropical tanks, even when it comes straight from the tap).
I do not recommend other people to do this, because it is very risky (especially when you're tap water is just of avergae or lower quality), but for me it worked out all right...