Drooping leaves and pale leaves on seedlings.

I just started a SSH, Blue Kush, and L.S.D. in 5 gallon DWC buckets. This is my second grow, my first went off without a hitch.

The seedlings are perhaps two weeks old, they were started in rockwool cubes and transferred to the hydroton as soon as the taproots started popping through the cubes. Everything seemed to be going smoothly until the last two days when I noticed the SSH is droopy and turning pale in color. It's worth noting that the other two have sizable root systems which have pierced the bottom of their baskets and grown into the nutes (into a light nutrient solution, say 100ppm), but the SSH has yet to do so. In the mean time I have been keeping the hydroton moist with said nutrient solution so that any formed roots don't dry up on their route to the solution.

Two days ago I switched my light (600w MH) from 75% power to 100% (it's about a foot from the plant tops), this resulted in a climb in temp from about 78f to 84f (temps at night have been around 70f) and I have noticed some slight curling inwards of the leaves on the other two plants so some heat stress is apparently taking place. Also, the humidity has been low from the start of the grow (30% app) which I know can cause the drooping, but not the paleness.

Interestingly, in my last grow I tried SSH (in soil), but the damn thing just wouldn't take off, clearly this is a more finicky strain than the few I grew last time around...any help would be awesome.

Here's a pic from the top, I have another taken from the side to upload but I keep getting an error message...

Scratch that, just restarted my computer and all is well. Here she is from the side:

A couple things that could help.
Your 600 watts could be much farther away and your plants will still grow fine. 2.5 feet would be fine. Theyll grow into it soon enough in hydro.
If the roots havent touched the water yet are you top feeding the rock wool or just the hydroton? And on watering, are you feeding the nute solution or just water?
And if you just cranked it up to 1000 watts at a foot away death is coming. 1000 watts can hang out like four feet away with less issues than 1 foot away. Good luck.

Thanks for that. I've heard that HID bulbs hanging so close to seedlings isn't necessary, but it didn't cause any problems on my first grow (the cooltube makes for no difference in temperature whether the light is higher or lower, the whole room is a steady 84f). I was under the impression that you could never give your plants too much light, but with that said, I'll move it up a few more feet. Seeing as this issue started when I cranked up the wattage, I think you may have figured out the problem.

I'm feeding her that same light nutrient solution that is in the bucket below her, again, about 100ppm. I water the whole basket rockwool and hydroton (I could only find the 6" baskets which means there is alot more hydroton for the roots to explore before finding their way to the bottom), I do it about twice a day (whenever the top looks bone dry) since the heat issues started. Maybe it's the hydro equivalent of over-watering?

So I moved the light up about to about the three foot mark and switched back to 75% power. Whereas you may not be able to give your plants too much light, I do know that they do need time to adjust to brighter lights. I'll slowly acclimate them to full power.

Off topic, I noticed something peculiar. At 75% power my seedlings are receiving around 7-8k LUX (according to my light tester app. These apps are VERY handy, if anyone is looking for one of these, I made a relatively comprehensive post about useful cannabis related apps that seemed to go largely unnoticed a few weeks back...), but with the light at 100% and at the same distance the LUX jumps up to near 15K! It's funny, I thought I noticed more than a 25% increase in brightness when I switch from 75% to 100% power, whats up with that? Whats a good LUX for seedlings?

Also, the SSH is in a position in the room that gets the most LUX, so maybe the light is the issue.

One last thought, perhaps unrelated. On my last grow, the cotyledons didn't yellow and die until the plant was massive, the stem on my largest was perhaps twice the thickness of a pencil before they started tearing off. I started feeding those guys pretty aggressively early on, they seemed to like it (no signs of burning) and so I kept the ppm high. I notice now that my SSH's cotyledons are turning slight yellow in the center and the others are still green.

Could the fact that the plant is already heavy into it's food reserves mean that it is somehow underfed? Is wilting and paling a sign of underfeeding or a deficiency of some kind? Or is early cotyledon death simply a sign of a sickly plant?

The light can be too close. That's why you start seedlings in shade and not direct sunlight, or the direct sunlight will kill them. I think they need a tad more nutes, the light farther aaway

I gave her a pretty strong feeding (250ppm), I figure she will either recover with signs of burn which I can fix, or she won't in which case it is something else. She's looking less healthy today and growth has almost completely stopped, I figure I have another 3 days max to figure out what is wrong before she is gone for good.

Anyone ever grow GHSC's SSH? Anything come to mind about this strain that I should know (is she nute, heat, or humidity sensitive)? I've didn't have any issues with my other strains, but the others were all hybrids, this is my first sativa.