What can cause inward leaf curling/clawing?

It's a shame you don't have a diary up, I'd love to see how this progressed. Looks like reverse canoeing. Some leaves look like they're trying to flip over like when lights are too close. I don't think it's light though. Do you still run your recirculating pump(the "R" in RDWC)? Maybe you plant's base is staying too wet. If your roots reach the solution you don't really need to dump water at the base of the plant. I don't recirculate even with young plants, generally the humid environment of the rez is enough to promote root growth. Do you have a good, strong O2 pump for your rez? Could be a case of low oxygen. If your sure everything else is in check(pH, no nasties growing in rez, etc) those are the things I'd consider.

Can't be lack of water if you are growing in RDWC! Looks more like over feeding to me...........try reducing the strength of your nutrient solution. Blue Gelato, being a Sativa dominant strain, will have a lower need for nutrients than your typical Indica based hybrid.

thats a big sign of stress indeed. Some causes may be that the environment is too warm, which will dry out the media and the plant will not have enough access to water. Another possible consideration is the humidity of the grow space: similar to upward pointing leaf tips, if there isn’t enough humidity in the environment, the plant will wilt and you will notice the leaves droop and point down. So make sure your grow area stays under 86 °F/ 30 °C, and has a comfortable level of humidity (between 40%-65% depending on the stage of growth). Make sure that you’re watering and feeding your plant enough so that the medium doesn’t dry out and cause root damage.

Either silver bullets or horsetail steeped water for organic, that will sort your roots out dude

Something wrong with roots? Seems like too much competition in that canopy too, but 2d image can be an illusion too.