Ranch3r, I grow in nothing but Coco, and I am already pretty sure what is wrong. But Need more info to know for sure. What nuts are you using, how much do you add per gallon, and what PH are you adjusting it to.
AND NO!!! you can not over water in COCO, and DO NOT LET IT DRY OUT!!! This is Coco, not soil!!!! Do not take advice from soil growers. They know Soil, but will kill peoples Coco grows.
Also, leave them in 16-20 ounce plastic beer cups until they are about 10"-12" tall. Allowing them to set a nice root mass before transplanting them to larger pots. 6-8 liter pots or grow bags are large enough to grow nice sized plants.