I am having a nutes problem, the leaves are a much lighter green, and i think i should flush before starting 12/12 in 1 week (so flush then mix up a transition to flower, then grow for 1 more week, then on to flower) how do i flush a ebb and flow? just fill the res and let the pump cycle for awhile? how many times should i change out the res? and how long should i flush? a whole day? a couple of hours? and should i only use ph'd RO?