I currently have a ebb n flow system and use advance nutes and love da results. I am starting a small little project with a dwc and just ordered the perfect ph sensi a&b and hobbyist bundle. But to answer your question Advanced Nutrients guarantee these results with r/o water, not saying it...
havent really taken a measurement lately but im gonna say about 24 inches using a 1000w bulb, its on a digital ballast that i can bring down to 600w cant get room temp any lower den 80f and dont have no room to move light until i move my grow room else where!