The rockwool is totally inert, so there are not really any nutrients and the seedling only has enough in the embryo to support germination and a set of cotelydon leaves...so once they will have their first set of true leaves you should be giving them a very mild complete balanced nutrient containing n/p/k and all trace elements. I recommend 1/4 strength General Hydroponics Flora series in a 1/1/1 ratio. I would also add some Technaflora Root 66 or Advanced Nutrients Jump Start at half strength to really get them well established prior to going in the system and for the first week in the system. :thumbsup: