What's wrong with these plants

[AqPoseidon]

What could be the issue of these plants? Strain: Wappa
8litre pots, Plagron Royal mix. Sanlight q300.
The cuttings grew healthy fo three weeks after transplanting them from rock wool cubes into 8litre pots with royal mix. Since three days they changed into this (s.b).
What could that be?

 

[WeedHopper]

Hard to tell but it looks like a Magnesium deficiency.

 

[pute]

Bet you aren't using cal/mag at all. Also plants look like they could use some nitrogen. You might introduce yourself in the introduction thread and tell us a bit about you. Then come back and tell us what your feeding and water schedule is along with what you are using and we will help.

 

[WeedHopper]

I agree with Pute. Nitrogen might be needed also. Whats your PH?