Just a quick look at the current state of the lettuce.  The six week plant (facing forward) is doing really well.  This is after picking the rear leaves three times.  On the five week plant on the right, you can see the post-picking bare stalk.  This plant isn't doing quite as well.  I have been trying to keep the calcium in the nutrients boosted, but the there is still a little of tip burn on the leaves.  Optimal fertilizer levels are still a work in progress.  While the front and left are buttercrunch, the green leaf lettuce on the left and back of the system do not have significant tip burn.

This particular buttercrunch lettuce seems to like to grow vertically, even though it starts out horizontally.  The stalks take a 90 degree turn just outside the pod.  Other types have grown more towards the light than just up.