I am starting to think that you have a light feeder there, like a tropical that is perfectly happy in poor sandy soil without much of a food source. I'd raise the lights a couple inches anyway- a few moments isn't QUITE enough to gauge heat and high temps in a time of stress aren't all that great. Once you see that new growth is healthy, drop them a bit closer.
It's good you are flowering them immediately, because tropicals get HUGE and will likely triple in size. In soil, potbound plants show that leaf shape but in DWC I don't know how it goes.
There's one last thing that frequently causes the leaves to look like that... not nearly enough air circulation, or suffocation from overapplication of an oily or waxy foliar spray.
So this is your project:
Bloom ferts, starting at the ppm you are running now and then gradually increasing until you see the start of tipburn, then backing off.
LOTS of air movement- you need a strong exhaust and unobstructed intake. Big plants need to BREEEEEATHE!
Check that the roots have enough space- you might have to look around the internet for this.