Recirculating DWC questions

[n3xus210]

Hi all, I am brand new to hydroponics and I chose to start a Recirculating DWC as my first system. I have read everywhere I can find and still havent come across a good article explaining how to change the water in a dwc system without killing the plants. How long can the roots remain in the air while the old water is drained. Does the new water have to be heated to the old waters temp first or is cold water okay? Does all of the old water need to be replaced? Are there any tricks to changing the water? Also, I am planning on starting some clones in rockwool then transplanting to a netpot filled with expanded clay on my dwc system. How far should the water level be from the bottom of the rockwool at first? Do I Set the rockwool right on the net pot and cover with expanded clay, or do I put some clay down first? These might seem like dumb questions but I just need to clarify. Thank you