zeitate's grows

I have a problem with one of the plants. Some of the leaves have turned to a yellowish colour. Please check the attached pictures. What do you think it is?

She is 19 days old and I just moved here into the system (along with the other plants). The other plants don't have any of her signs. She is the biggest.

Haven't posted in a while.

Here are the ladies. They are in their first week of flowering and 5th week in the system. For the moment I have 2 x 600w agro Lumii lamps turned on. In about 1-2 weeks I'll turn on the third lamp.

Also moved some clones in the system a few days before I started flowering. Don't really know what will happen to them. I'll guess they'll grow a little and then also flower?! We'll see.

I've decided that after I'll harvest, I'll regenerate them .

Started the 3rd week of flowering yesterday.

Hopefully it's true that they stop growing and concentrate all their energy on flowering production from the 4th week onward because I have only 35 cm left until they touch the lamps.

I stressed myself up a bit this past week about air humidity, but I've read that in using an aeroponics system a level of 60% to 70% humidity is generally ideal for most plants. Still trying to find some more information about this.