Hey bro; Sorry to hear the bad news. This is more commonly referred to as "The Claw" because they look like claws/eagle's talons. The culprit could be a number of things including but not limited to PH Fluxuations/inconsistencies, Nitrogen Overnuting and/or heat stress. The easist/first thing to do is eliminate high air temperature as the culprit, anything above 85 without CO2 could make them curl like that.
The 2nd most easiest is to determine how much nutes are in the res. Most nutrient solutions have higher-than-advertised nutrient levels and when following full dilution mixing instructions, you could easily over fertilize them. Determining how much PPM's of nutrients to give them depends on their age and strain. Your picture looks like she's well into flower, and she could probably handle up to 800 nutes with room temps.
The 3rd most difficult to determine cause of the claw could be PH fluctuations and it's electroconductivity level. I think 5.5 - 6.0 is optimal in hydroponics. and 6.0 - 7.0 is most optimal for soil.
I am only able to help because this has happened to me; I don't believe that it hinders bud production too much, but it sure is ugly to look at. Leaves should ALWAYS be reaching up towards the light.
I was also told in another thread that the clawing is normal sativa flowering. So fuck, now go figure lol, well best of luck to ya buddy.
I also forgot to mention that "IT MIGHT BE" that it's not getting enough Oxygen to the root zone (but that more or so makes them wilt).
