yellowing leaves

I'm getting some yellowing leaves in my plant which is just 3 weeks old. It was only be affecting 4 leaves however it looks like the green color is starting to fade out of other leaves. I have no idea what is wrong, can anyone tell whats wrong from these pics? thanks

What are you feeding them? Probably need N...

Lousy soil or feeding. You're just off base with something basic.

I think your plant would love some nutrients, rich in nitrogen. Also add some cal-mag if you're watering with RO. Remember to start with just 20% to 25% of the recommended dosage. When do you plan on transplanting it?