3 weeks old yellowing on some leaves

Hey guys, here I have my little plant that has started to develop some problems. She's about 3 weeks old being grown indoors. I'm using rapid nutrient system and she's under a mars hydro 400. She has had this problem since she was about a week old but now it seems to be getting worse. Any help would be great thank you

What are you feeding it. looks like she could use some cal mag

Rapid Nutrient System?, what's that.. Did you feed the plants before the first three weeks? What type of soil are they in, and did they start in a different soil? Have been you putting anything on your soil such as Molasses or Coffee Grounds? I see terrible pH fluctuation signs and from experience I know what causes that but the response depends on the why.

The tips look like they maybe burning ??

Back off the nutes -20% , its too young to have burnt tips and i think its over fed.