curling, browning leaves

This is probably a pretty common question... but see my attached photo. My little plant leaves have started to turn brown and are curling under. This is spreading to ALL leaves, including some of the little new ones.
Background:

1. A few days ago, I moved this little plant from soil to a hydroponic ebb/flow.
- I rinsed/sprayed the roots carefully to remove soil.
- water/nutrient: 1/2 hour, 4-times per day flowing
- nutrient mix - at the low end right now, rated for "seedlings"
- light: 20 hours/day metal-halide, about 12-16 inches from plant

Note that I am using low nutrient at the moment because I have a few very small seedlings in the same ebb/flow system.

Any ideas on the cause? or suggestions on how to proceed in tweaking what I'm doing?

Thanks!

I having exactly the same problem, identical leaves.

I run a recirc system 24 hours a day with a dripper, expanded clay suspended in a bucket, never more thaqn half an inch of fresh solution in the bottom, plenty of air, roots are suspended between clay and bottom of bucket

Ran 18/6 light cycle

Hydro Nutes fairly high TDS though.....

A few notes...

the curling browning leaves don't seem to really hurt the plants so far. It only affects the larger, older leaves - the new ones are coming out fine.

Also, I did find a good resource with lots of pics, one of which seemed to match. It said it was a magnesium deficiency. However... some descriptions of these leaves say it is over-fertilization.

Some ood resources/charts with symptoms, and causes:
Troubleshooting marijuana growing health problems.
GanjaPedia - Marijuana Growing Guides...Marijuana Nutrient Disorders

For now, things are looking good. Just about to start flowering.

nt sure of the full problem but the best thing 2 do wud be 2 clip the lower leaves!