They look good, makes me want a nice salad. Which ones are limp? I also notice you have seedlings in the same system with the 30 day plants. The
nutrient strength may be to strong for the seedlings, or weak for the larger plants. I don't know how much volume of water (nutrient solution) your using for plants, but 4 weeks is the max length of time I have ever gone between changes myself. I was about 3/4 gallons of nutrient solution per plant. But when they got to be about the size of your 30 day plants, I upped the nutrient strength from about 1/2 strength, to about 3/4 strength, and changed the
nutrients about every 2 weeks. Though all my plants were the same size. regardless, your plants look pretty healthy from the pictures.