If you have an ec tester check your runoff and see how high your nutes are coming out but if your growing in soil then flushing doesn't really make much a difference unless you had way to much nutes in there. I like to take mine when the runoff is coming out under 0.4 ec 200 ppm. My water has 100 ppm so that's 100 ppm of the nutes I added still in there. .Cheers