My only problems with GG4, was from using coco, which I hate, but still use for mother plants, and making seeds. Every grow turned out different, and the best grow I micro managed the feed PPM/PH and the runoff. Very important to not over feed it. Start at 300PPM and end at 600PPM, never over 650PPM in coco. Have not figured out if numbers should be different for hydro, where I am getting hollow stems, which never happened in coco.
Im at 1.4 EC with my GG4 that's my stopping point..... as far as pushing the nutrient profile....Im in coco and i know i have a couple of hollow stems ( I snapped a top during training and it was hollow as can be...) they look healthy....... just waiting on them to swell up a bit....