Shagrathanswered grow question 4 years ago Hi there!
With hydro you can flush shorter time if you change the whole rez to plain water. I think 5-8 days is enough because in hydro you take all the nutes straight away and the plant starts to use the nutes stored in the leaves right away but in soil you have to flush the nutes off from soil or water with plain water so the plant uses the nutes from the soil first and then from the leaves.
So I say 5 days before harvest change plain pH'ed water and keep checking ec and change again if it rises too much.