I am using the advanced nutrient s 3 part non ph perfect nutrients, and tap water. What im wondering is, when i check my ppm reading and I need to add nutes, how do i know of which nute to add?? or do i mix them all at an equal amount to get my desired ppm?? What if my tap water already has a ppm reading of 250 ish?? Also wouldnt the ppm of the nutrients that im adding totally change when i add to the resevoir because the ppm of the res water is different then what i am adding??? How does the math work??