Like i said, start with half of what GH recommends. Sure coco and soil is different, but when the soil runs out of nutes it is essentially a inert medium at this point meaning is has no nutritional value. Then you would feed like it was an inert medium the only difference being ph and you probably dont need cal mag as coco needs it for proper ionization or something, cant remember the exact science of the top of my head. Or you could try and figure out the correct nute strength yourself by trial and error. This is what a lot of our growers do. Start half and increase slightly until tip burn then record what you fed.