I'm wondering why my girls yellowish and how ...

Your ladies look pretty happy , the reason they're light like that is nitrogen . During the veg cycle your plants are going to use alot of nitrogen. You've done well by not over feeding your plants because it's always easier to add a little bit then try to correct problems . I'd say keep doing what you're doing but make your nutrient solution abit stronger I suggest 1.5ml/l - 2ml/l until your leaves get abit darker not much but abit . I also noticed that you aren't using a calmg solution . It's very important that in a soiless medium you give them weekly doses of it . The problems you will run into with calmg def are the stalks on leaves will start to become red/purple , the veins on your leaves will become yellow in colour and then take over the leaf . You will also notice your plant will be slower to grow and later in flower it impacted bud development , potency and yield . So Calmg is super important in all stages . If you were in soil it wouldn't be so bad but soiless and hydroponic systems neeeed it . Other wise your plants in good shape just a few minor things to correct and she will explode in growth and become a monster . I hope this information helps you on your journey ! Happy Growing!