You've got way too much light on them.
I can't tell some details from your post or pictures, but I'll assume:
- your 100 watt equivalent bulbs each produce 1700 lumen
- your 75 watt equivalent bulbs each produce 1100 lumen
- your seedlings are 6" from each bulb
If that is the case then you are giving you seedlings 241,000 lux. If you've got them four inches away from your seedlings you are giving them 542,000 lux.
This is WAY too much.
Cut your lighting back to 1 of your 75 Watt equivalent lights four to five inches directly over each seedling. This will provide between 100,000 and 150,000 lux, depending on the exact distances to both lights.
You really only want to provide between 100,000 and 120,000 lux
(http://en.wikipedia.org/wiki/Daylight). The plants can handle a bit above this (up to 150,000 I would say) without getting light toxicity, and will do fine a bit below (down to 75,000, I would say) without stretching.
Here's the signs that I've seen before of over-lighting:
- Leaves twist and curl or point. Top leaves, especially new growth will often point up. Bottom leaves will often try to point down. The leaves are attempting to get out of the light the best they can.
- Slow or no growth. To use the well known saying: it's like drinking from a firehose. Too much light prevents the plant from properly absorbing the light. There's some research out there on plants in general about "excess excitation" causing "light toxicity".
- Leaf color turns light green, especially in new growth. Also may be bleached white or if heat damage occurs, brown. The change from dark to light green is a result in decreased chlorophyll production as a response to excess light.
The lighting is your current problem. But also do as suggested and hold off on fertilizing for a little while. I start fertilizing at 1/4 strength on week 2, and move up to 1/2 strength for a few weeks. Others wait even longer.
Make sure you are watering right, at that stage in that size pot, I usually water once every five days, but don't rely on that schedule for your own plants.