Little help?

So my plants is 20 days old.
I feed the each one today with 500 ml clean water, 6.9 Ph.
Next feeding is about to 2-3 days later depends on how hot is weather and how dry is soil.
In the next feeding I'm going to start using a fertz on them as you can see on the pic.
Which ones should I start with?
With how much?

Thank you...

 

Thanks!

 

So today, I started nutritiens with go root and thrive, 1 ml per one 500 ml clean water with 6.9-7.3 pH.
Öne of them seems start the preflower when another feeding comes, should I start feed that one with bio's? Or just wait the g.o's till I'm going to full dose on them?
Any suggestion?