The only thing I would disregard would be the ppm's in Tapwater if under 150. If you use tap water higher then 150 I would go to the water companies website and down load their profile of the water. Most nute calculators have a section to plug your waters elements into. The calculators will give you a good but rough idea of your rez's profile. I would go with what my calibrated meter tells me as far as ppm's. I use the calculator to adjust or play with my nute profile,I use the meter to see where I am at,then use the Plant's looks and how it reacts to dial it in. JK