Curious...why no shots of the whole plant? How many plants do you have in each pot?

Depending on the perlite content, (or lack of perlite) a 5 gallon bucket will retain water like crazy. You do have drainage holes in the bottom, right? When you water, do you water slowly, or just splash it in? Does the water flow immediatelly out of the bottom? Does any absorb into the medium?

During the hot dry months, I have to water my 5 gallon buckets with 1/4 to 1/2 gallon daily. But I do use extra perlite to avoid oversaturation.

6" is too far, get 'em closer, or add more lights, or think about an HID system. (metal halide or HPS)

Why no nutrients yet?

Whatever size container you are in...always keep soil to within an inch or two of the top. The top of the rootball needs air circulation too. Just be sure to leave enough room for watering.