Hi jaygee, Im a compleat novice with any plant growing, but your plants do look a little small for 3 weeks, here is a pic of mine at 3 weeks may be its because I use soil, I dont know? I am struggling with the one I have in flower, but it is my first time so im learning loads on the way as so will you, sorry i cant give you much advice on feeding as your medium will be different to soil, I think? but 1/4 strength seems to be the common advice Iv read on RIU to start feeding at every other watering and as you get to full strength every 7 days the new growth will start to look yellow if you over do it and the older growth yellows if you under feed well thats what I have found with my grow