Hey bro I think I had the same problem with yellowing and slow growth in the beginning, it might be that you're feeding too lightly. Now this is based on Canna coco but it might be the same if your coco has no nutes. Try feeding at .8ec from day 1, i've tried it once with good results and now trying it on my 2 day old seedlings and so far they're liking it.
Another thing is proper dry out times in the beginning. What im doing now is feeding 12oz of water@.8ec on days 1 and 2, then I'll let them dry out for two whole days, then watering 24oz @.8ec on day 5, then letting it dry out for another 2 days, by day 14 I will water once a day.
If you have root stimulators they will help alot too, i use rhizotonic it's good stuff.