i use a 70% coco and 30% pebbles for seedlingd and cuttings but by the time the have rooted well i have the mixture down to 50/50. the medium is light and airy and allows loads of oxygen to get to the roots when u water them. i have always use this mix and i have never had any problems with root rot aor any other things , its really hard to over water asthe mixture will dry in a couple of days , allow thats has been with the kush i was growing , which i think is made from steel anyway .