Should I change course.. pic to support

Hi Guys,
I'm having issues identifying the causes of my girls issues, which in turn is causing me stress. Combined we are having sleepless nights which is only amplifying the issue.
Do i change course and reverse current feeding and water schedule....

1...12 girls from seed, 3 weeks young sitting in 3" rockwool on NFT table.

2....Water temp hovering around 20c but can get up to 22c during afternoons.

3......Ph is staying constant at 6.1 even tho i frequently drop it to 5.5/5.6 before lights on but jumps up but never goes above 6.2

4.......PPM's were up around 600 and noticed a little burning (i thought) so reduced it back to 200'ish, using Canna A ÷ B agua veg.

5.....Watering schedule is a bit erratic whereby i let them run for an hours or so in the morning once they wake up with water temp at ideal temp 18c. PH 5.6 @ 200 ppm's. Every other hour thereafter for 30 to 40mins at a time.

6..... Root mass and structure is fine and plenty full. Snow white and healthy.

7.....Room temp stays at 26c/28c by day and 20c'ish by night

Since i dropped the ppm/ec they seemed to have picked up and start righting them selves with reduced burning and looking healthier. However today when i popping in to say morning and make sure everything was fine i noticed they looked sad with some buried signs and discolouration on over 50% of them. Pic attached
Upon research i done today, viewing a page i found on here showing deficiencies on leaves, my girls i think are showing very similiar signs.
My $1m question to you guys is.
Do i have a deficiency or over zealous feeding regime or perhaps a different issue which I'm missing.
Input and advice would be greatly appreciated, might even help me sleep tonight.
 

Attachments

Roots are excellent, snow white and plenty growth each day.
Ph hovers around the 6.0
I tho it was nute burn so reduced ppm from 600 back to 200ish...
I thought originally i was over doing it with the feed as there are from seeds which suggest they dont require a lot of feed in there first month ....
 
Do the pic help?
I'm struggling to identify which issue i have, the others are now starting to look a bit yellow'ish also ... your thoughts or suggestions are appreciated Renfro
 
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