run-off water's ppm

Hey friends,

I'm growing using a 'basement blend' coco, which is a soil-less medium. I had not flushed (leached) in 4 weeks, and when I checked the ppm of my run-off water, it was off the charts.

So I flushed. The day after, I watered my plants with 1000 ppm solution and checked the ppm of my run-off, and it read 1500 ppm.

Based on the ppm of my run-off, at what point do I know I need to flush?

Thanks,

ppm's of soil runoff is a pointless number. There are so many pieces of your soil that it can't be used as an accurate reading