what...is...happening?

Ok I'll try to help as much as I can with info.
Two girls: Tegan and Sara from cheap mexican schwag bagseeds
Hydro, ebb/flow, 15 min flood every 2 hrs, aqua A&B, NPK 0-13-14 flowering
1000W HPS cool tube, 6" planters with hydroton clay pellets

They will finish their third week of flowering tomorrow. Tegan has always been well and robust, but Sara looks like she is definitely hurting. Her flowers and most of her leaves have a very distinctive curling at the ends, the tips are brittle and break under pressure. Lower leaves look very bleached/yellow-green compared to Tegans very dark green.

Tegans topmost part is 19" from the glass of the tube, Sara is 17".

There have been no critical issues, pests, bad nutrients, missed feedings, miscalculated nutrients, or environmental stress. Tegan is doing just fine, and Sara is going crazy.

What really worries me now is that one individual flower on Tegan is starting to display a curling at the very ends of its leaves akin to Sara. I don't want Tegan to start hurting too.

Here's an album that should help, all the shots have descriptions so you know what you're looking at. If it asks for a guest PW, its Greenie with a capital G. Take care and thanks!
Login to a private Photobucket.com album

It looks a lot like heat stress but from what your telling us it can't be heat stress. I left town for a month once and I had set up an auto watering for my soil mother plant. When I got back the auto watering thing I had set up had been working but, it had not given the plant enough water. Enough was given for the plant to stay alive, but it suffered damage that looked a lot like yours.

I would check the water lines to make sure that Sara is getting properly flooded and drained. Then move it 6 inches away from the light and put a small fan blowing directly on her. Then get some florakleen and flush like mad and give some fresh nutes. There could be a clump of hardened nutes in the hydroton, poisoning your plant. You need to dissolve it and flush it out.

Last thing i think it could be is damage to your main stem. Inspect it well, if you find something seal it up with some store bought stuff or superglue.

Good luck

I've never seen anything like that personally, but I think you should be feeding with some nitrogen. Nitrogen helps keeps the leaves green. Also, do you know what your PPM/EC is? That and your pH would help diagnose the problem as well. I know overfeeding causes leaves to curl like that but I've never seen leaves curl up like that.

I would say for right now, I would flush with pH water only until we can get some more info and figure out what the problem is for sure.

fill out form in the problem section and then you will get definite answers and not guesses...the experts can give you without a doubt an answer if you can provide them the information...i had an issue like that and it was a jacked up ph...also i thought i saw root rot...but until you fill out the forms all you will get is "it could be this..." or "it could be that..."
I'm not trying to be mean...i'm tryin to make sure you get good information as quick as possible so that your girls**hopefully** can make a full recovery.
Good luck

I think there is nitrogen in aqua A&B.

Looks like a ph issue to me. And cman is right.....it's all guesses without good info.
Any chance for some decent photos without the hps light?