nute burn or heat stress...hard to tell

Hey guys. From the pics you can see I'm having some browning on the middle set of leaves of my WW. I recently transplanted 3 weeks ago from a solo cup of FFOF with ~15% perlite into a 5 gal Home Depot bucket (same soil), w/ holes drilled in the bottom for drainage. Before transplanting, I watered (plain filtered water that sat out for a day) the soil in the bucket and let it drain for several hours. My lighting is HPS 400W air-cooled about 8" away. Temp hovers around 76-80F with an oscillating fan and fresh air coming in.

I watered it for the first time after 12 days post-transplanting with 1/2 strength FF Big Bloom. I then added a 26W CFL lamp (6500K) about 6" away.

I've done a bunch of reading and found that pictures of plants with nute burn and those with lamp burn are very similar. Its hard to tell whats going on with my baby.
Any opinions to which it could be?

Thanks!!

Looks like a deficiency or lock-out problem. I would check the pH runoff and go from there. If pH is OK, I would start looking into magnesium deficiency as the first pic seems to look pretty similar to lacking magnesium, but could be caused by incorrect pH... so pH first, then worry about nutes if runoff and feed are OK pH-wise. I only say magnesium because the dark veins on the leaves and interveinal chlorosis with the spots, but I could be wrong. hope I helped steer in the right direction.

PH Lockout. Check your PH!!! Check the water you're feeding and the current soil PH. Probably need to flush heavy with PH'd water.

^^^agreed looks like nute burn

Its light/heat burn, get the 400w at least a foot away even with cooltube, back the cfl off to.

Hey all! Here's an update...
I moved the lights away and the browning still happened (pic below).

I skipped nutes for the last watering (last Wednesday) and still it was browning by today. Again I watered with no nutes. I feel like she's a dwarf--she's only grown less than an inch in one week! My neighboring plant (unknown strain/sex...free mystery seeds from Nirvana) is growing about an inch a day.



Also, speaking of the second plant (shown below) can you confirm that its a female. I'm not sure if 4 weeks post-transplantation is too early for sexing.



Thanks alot for the help guys!

damage is done nothing will fix the brown thats already on the plant just have to watch the new growth for the same issue