Need help with diagnosis

Hi all,this is my second grow.I'm doing 10 white widow which are now on day 8 of flowering.I gave them veg nutes for the first six weeks(Biogrow NPK 4.0-3.0-6.0)and everything was great until I put them into flower 8 days ago when i gave them some premixed Dutch flowering nutes(Biobloom NPK 2.0-6.0-3.5 and Bio Top Max bloom stimulator NPK 0.1-0.01-0.1)at a quarter strength on top of the veg nutes as per the Biogrow chart.I only gave them half a litre of mixture(they're in 18 litre pots) and within half hour most of the plants were drooping.The majority of them pulled through no problem except for a couple whose leaves started to curl as per pics.Even the new lower foilage doesn't look too clever either and even when i give them the slightest bit of water they start to droop.
Do you think that they've been overnuted and I've burnt the roots somehow,I've given them just fresh water for the last week but the leaves are still curling.Any ideas??

check if they are a root bound, if not check ph of the solution after you've watered them, do this by overwatering one of them until it drips out of the bottom of the pot. test the water that drips out of the pot, if this is not it it's the ppm so check the run-off for both, if you are still having problems make sure you've mixed your nutes well and in water that is not too cold or too hot as this will affect the mixing, which reminds me if the water is too hot the plants will not take it up. Also you may be over watering. You should let the surface of the medium to dry not the whole pot just the top 1 or 2 inches as this will allow proper air exchange in the root system. if this is still not it get back to me in greater detail and I'll try to help out

Thanks alot for your comment.ph is dead on 7 as it's straight out of the tap and i'm only giving them a little water at a time cos i overwatered on my first grow so i'm a bit cautious with that.Some people say that the ph should be 6.8,do you think that it'll make a difference if it's slightly over?Sorry for being naive but how do you check whether they're root bound and what's ppm?