Out of ideas ...

You have the lamp very close.

Look lke they need a good deep watering until run off and a lot less feeding...........too dry and borderline nitrogen toxicity is how they look to me. Without a diary, it is hard to be more specific.

How hot is your tent or is your light to close , mine done this when they got too hot but bounced back when i cooled the tent down

What kind of light are you using?if your using a HPS light I think there too close to it,another thing is at least with my grow now all my ladies one hour before lights out droop like that but from my research there "sleeping",basically they had so much light they can't take anymore and go to "sleep" to recover and they do,from the picture u gave I'd say there too close to the light,I might be wrong that's my guess tho

you are watering wrong. i can tell by the description of your actions. stop trying to give a volume of water you choose.. that's not what is needed. 1/2 liter of feed won't saturate the entire pot... so all you are doing is piling up minerals in the substrate. soikl -- water until saturated - minimal runoff can ensure this... no dry pockets. adjust frequency/concentration of ferts as needed, but always saturate entire pot.. if it's too much you can either reduce concentration or reduce frequency of fertigation.. it all adds up the same in the end as far as how much of any molecule is needed relative to your garden's variables. Wait for top 1" to dry and repeat. (weight of pot is best indicator and will result in a consistent volume needed... dictated by substrate characteristics and size of pot... not something you randomly choose.) soiless. water with fertilizer every time with a 1.3-1.5 ec concetration of well-balanced mix with 10% or more runoff... the runoff ensures conssitency of concentration in soilless substrate. (if soil is completely devoid of original amendments, you can treat it this way too, otherwise you have to consider what it already has... soil is more about supplementation and soilless is about a 100% fulfillment of diet.) Probably a combination of bad watering habits and aslightly off nute mix... get the watering habits worked out first, then see what problems remain.

root breathing problems I don't know what soil or fertilizers you're using, but a diary wouldn't be a bad idea to help you better... Anyway, let the pot dry out really well; it should be super light, then add mycorrhizae and humic acid at the first watering without any additional fertilization. See how they react and do it a second time, letting it dry out really well. The heavier leaves might stay like that for a few days, while the new sprouts should be reaching up...

Around 21-26 degrees, quite consistent all throughout

What are your temps like. If its to cold they will look like that.