ppm measure the amount of nutrients in the water. Closer to Zero the less nutes in water, higher the number the more nutes there is. ordinary water would roughly have between 0-400 ( depends on your city standard) Unless you use bottle water or another system). PPM doesn't add up.
a general guide is that you use no nutes(just plain water ) from 0 to 2-3 weeks. 3-4 weeks you use 1/4 strength(200-400ppm), then 3-4 weeks 1/2 strength(500 to 700ppm) and 4-5 weeks full strength(800-1100ppm).