nutrient input

Just germed a few in coco. Growing outdoors in pots how soon before I should start feeding them the water soluble npk I got

if you're in plain coco or mostly coco, you should already be feeding them at least a light mix. Never use plain water with coco.

The way you say water soluble NPK makes me think you are using something ill advised. Make sure the nitrogen isn't all from Urea/Ammonium Nitrate.

1/4 to 1/2 strength at first, but never just water unless flushing in coco.