I run 18/6. I have no scientific evidence to back up my choice of 18/6 over 20/4. I've seen it recommended by some of the breeders, but I've also seen some say you get more yield with 20/4. I've never seen a very strong argument for 24/0 through flowering. It is my understanding that most root development happens during the dark hours... but, how much difference a couple hours a night makes, IDK.