G13HxNYCD/Blueberry indoor grow

You decided to use your 400mh early after your t5. what made you decide to do that and how did you figure out the height to place the 400mh in the beginning and as they grow until 12/12 (ie dropping light w/ chains as plants grow, for example lower light 1 inch every 4 days or so then increase height of light in proportion to growth). Also is the mix you used for your seedlings the same as in your pots and what type ? what type of water (im digging for info on distilled w/ cal mag added) did you start nutes as soon as you moved to 400mh ? temps ? fan on temp control to use co2 pucks or just run fan during light cycle and hope pucks work. lots of questions sry but i give you props for the setup.