Yeah I'm going to have to agree here.. I wouldn't mess with them personally.. they look about as happy as any plant can be. I would just continue doing what you're doing feeding wise and not start adding a bunch of random crap throwing off your "hydro" balance you got going right now.. As mentioned above, the new growth will be slightly pale/yellow as it's developing. Perfectly normal. When you toss them into flower they will get really pale/yellow about half way through the transition but that is also pretty normal, so don't be alarmed when you get to that stage as well. The colors of the plant will change quite a bit throughout its life cycle, so you just gotta learn your particular strain.
Plants look great! Nice leaf structure! What's the strain?