What should my ppm be in preflower

i feed a consistent, well-balanced diet from start to finish in a soilless substrate. With soil, i might mix in some pH'd irrigations too. But, if getting 20% runoff waste, should maintain a healthy and fertile equilibrium for the roots... wait for top 1" to dry and no root rot or related issues. the most fertile lands in the world don't change their chemistry midstream. That doesn't necessarily mean it is the 'best' but it's a good correlation. Unless your tap ppm is really high, you'd probably be fine 600-1000ppm? i'd reccommend 700-ish to start and react to plants individually.