Auto seedlings yellowing

[Corogold]

Hello fellow growers. This is my 1st indoor grow 2nd overall grow. I have 9 feminized auto seedlings plus 9 clones. My setup is 1200 by 1200 by 2000mm eclipse grow tent inline fan 156cfm with 500 by 100 carbon filter and 2 small oclilating fans 1 just above plants 1 blowing around lower pots.and 800watt 4season luma led light. Im growing in canna coco plus professional fertilizer. Seedlings are 3weeks old now still on 3 finger serated leaves cotyeldons are now yellow top leaves light green. I gave them there 1st feed a week ago they were 2weeks old and i gave them quarter strength my nutes are canna coco A+B and canna rizoritonic for healthy roots.

 

[Corogold]

My problem is what would yous do if ya seedlings were yellow at bottom leaves and slowly working way up. There 3weeks old at 3 finger leaves and approx 6cm at hieght so are they siverly stunted i have clones that ive fimmed and toped aswell for backup what would yas do and any feedback on what i could or should do pleae help guys and gals

 

[Rwise]

Yellowing from the veins into the leaf is a sulfur definitioncy. Powdered water soluble sulfur is the answer to that.