When using coco as your growing medium, it is advisable to use a coco-specific nutrient. Coco-specific nutrients, such as VitaLink Coir, contain less potassium in order to take into account the potassium levels released from the media during the growing cycle.  VitaLink Coir is an easy to use one-part nutrient that's available in either hard or soft water variants and as specific 'Grow' and 'Bloom' formulas.