You need to use a nutrient that is high in P, medium to high in K with very little N.
And you need to stop all nutrients 10--14 days before harvesting to get rid of excess nutes (which can ruin the taste of the buds).
I like to add about 1 oz. of unsweetened pineapple juice to plain water during the last 2 weeks, to feed the mychorrizae.
