Cool,
Yea, i always flushed with plain ro water, kept changing it out till I was under 100 ppm.
Usually took a week or so. I recently found a product called clearex. I tried it on my last flush. I run it for 24 hours and then plain water. Worked pretty dam good.
What happened was the flush water went to under 100 ppm instantly. Like it washed off the roots, sucked out available nutes and made the plant use up what it had the last week. I am using it again today to flush the floro cab.
You can also use it during your grow, lets say you are moving from veg to flower, run clearex for less time like 1 to 3 hours then drain and add your new soup. Start slow, like 1/4 strength or it will burn but It removes the veg nutrients and gets it flowering faster. Or if you over nuted you can use it I guess.
Anyway, you might want to look into that.