How many weeks veg are you in? How big are the plants approximately? They def just need more food primarily the 3 I mentioned. You will be good in a few days. 600 PPM is low, idk what your PPM of your water is? But in established clones anytime after the 2nd week once they are rooted should have no problem taking up 800 PPM's of your bases and cal-mag.
I can show you a before and after pic of the same exact problem on some 2 week old cuts. The leaf hooking and mottling between veins that were light green. Its simple solution which is the need more food.
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Same hook shaped leaves with the blotchy light green leaves. These were rooted cuts that went into b2 coco mix with just water for about 2 weeks light nutrients.
So i fed them 800 PPM and this is them about a few days later. As you can see they have almost completely bounced back. One more nice feeding and they will be good.
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When Im in veg I start around 6-800 PPM WEEK 3 than go up about 100 PPM until week 6 usually maxing out around 1000 PPM before I flip.