IMO your input needs to first be lots of pHed (6.0) distilled or RO water to rule out the possibility that your coco needs to be washed of salts (Not nutrient salts, natural salts that exist in some brands of coco coir). Then you need to feed, as coco coir is inert. You are currently watering with just water, and the first set of true leaves (the serrated ones) have appeared. So its time to feed. Lightly. Adjust incoming pH to yeild a runoff that is around 6.0.