I'm new to gardening and hydroponics, but I am successfully growing Black Seed Simpson and Red Romaine using the General Hydroponics Flora Series. I mixed the nutes as it says to below, as found on their website's FAQs section:

"The proper ratio of each Flora Series nutrient depends on the crop and the stage of growth (look on the label for specific recommendations for different crops). However, as a rule of thumb we use the "1-2-3" ratio:

For seeds, cuttings, or delicate seedlings- use 1/4 tsp. of each nutrient to 1 gallon water

For the vegetative stage of growth- use 3 tsp. (15 ml) FloraGro to 2 tsp. (10 ml) FloraMicro to 1 tsp. (5 ml) FloraBloom to 1 gallon water

For late vegetative to pre-bloom stage- use 2 tsp. of each nutrient to 1 gallon water

For bloom initiation to ripening stage- use 1 tsp. FloraGro to 2 tsp. FloraMicro to 3 tsp. FloraBloom to 1 gallon water."

in your case, I'd mix them using the second mix (vegetative stage) but maybe a bit lighter, and see what happens.

Other things that effect how much nutes you need: temperature, the amount of light, and pH/PPM.

Although your lighting is rather sufficient.

Plants require less nutes when it's hotter, and more when it's colder.

Justin,

Wow great post! I agree with Justin 100%. It looks like you are only using one of the three mixtures they recommend.

Link for reference: http://www.ebay.com/itm/like/111601643281?lpid=82&chn=ps

I would like to say that nutrients are based on the person. You get a wide variety of comments from different people on what they prefer based on how or what they are growing. I personally like the General Hydroponics Flora Series.for growing anything; however, I will let a more specialized person weigh in.

EDIT: In taking a second look I would say that it might be a disease as well. Sometimes diseases come on from nutrient deficiencies. With the plants this small it might make sense to start over and just make sure the mixtures are right. I have found it difficult to start a plant with problems and get it to grow healthy (not saying it can't be done though). Can we get a pic of the roots?

What's your ph at, they look green to me. Just the pale green from inside the leaf to the tip, not yellow from the tip to stem seems like mg is getting locked out...twisting of the leaves usually always means ph is off, I'm guessing to high...I would flush out the res and clean it add water (if reverse osmosis bring it back up to 150-250ppm with a calmag product, with a touch of hydrogen peroxide for a couple days then load it back up with nutes, can't go wrong with general hydroponics they are great and don't rip you off. Remember even corrected it will get worse for a couple days so just chill out and go with what you decide, if you do to much it will never correct itself and even if it did you wouldn't know really how to correct it next time. Hey you said you were using the grow but your using the micros as well right, with the bloom...personally I run micro and bloom...no grow, equal parts..takr a look at the micro it is chalked full of N..to much can push your plants to hard and quite frankly can taste like sh*t....but yeah my money's on the ph.

Hey gh does have a step up for nutrients it is a grow and a bloom with no micro, has like a space ship on it...both lines are excellent though

What is your pH? How close do you have your lights? A HID light, whether
MH or HPS, will bake your plants if kept too close. I see some signs of that
in your second photo. How often are you flooding your plants?

Some
guys at my local hydro shop have used only FloraGro on lettuce just
fine. The plants looked OK but not great. It was a test on their part.
You'll most likely encounter some micro deficiencies. If you want to use
GH products I would be using MaxiGro for lettuce. It's a great
"all-purpose" nutrient. More difficult to mix up since it's powder but
way cheaper than the 3-part FloraSeries and frankly you don't need that
kind of flexibility for growing lettuce. I use it on all my leafy
greens.