I know this get's argued alot, but it never hurts to run a few gallongs through your soiless medium. Plants can burn in all mediums, so if they can burn than they are obviously able to extract more nutrients than needed out of the roots/medium. A flush is never a bad idea, there is a reason some weed burns your lips when joint smoked, and/or the ash is black and it won't stay lit. Sorry to those who disagree, but any veteran can tell you that with salt based nutes and hydro nutes in soiless and soil grows for that matter, a flush is vital to a smooth taste and burn. Always rid the plant of excess nutrients.