all up to you bro. i think most would tell you they flush with 1/8 strength nute solution or whatever else then clean system,renute right away. personally, i flush with 4ml/gallon hygrozyme @ 5.5 ph with my 0.22 EC tap water.5 gallons per each 6" netpot with 2"rockwool cube and hydroton. then renute immediately. i would not reccomend straight water feeding after flush mid grow unless absolutely necessary b/c of nuteburn imo