Well, unless you are very diligent, precise or lucky, this method is subject to poor performance due to small margin of error. If the lighting is low enough and if the tap water is high in nutrients this can work quite well, but it's a tedious method. Most here use some version of EI or PMDD, which are much easier, don't require testing and produces great results.
Not sure which theories you've read but many theories, including those on which PPS is based on often rely on the concept of limiting growth by limiting nutrients. This works fine unless the nutrient levels fall below their minimum thresholds, which is a constant threat. Thus the need to continually monitor nutrient levels and calibrate test kits. Very tedious.
Cheers,