you'll have to feed each watering with coco medium for a healthy and efficient grow. I would advise to go with canna nutes like a base one (their COCO A B stuff ,containing NPK) , some enzymes , calcium&magnesium(which is critical for coco growing) , ph down , maybe a PK Booster and a root stimulator which are optional. Many manufacturers make all of these. For AN, they have that stuff as well. Up to you choosing the brand but I heard Canna is a good one. I myself using Plagron nutrients for my coco grows and happy with them. You'll probably need the smallest bottles of those for 2 auto plants.go easy with nutes by the way,half of what it says on the bottle at most.