limpy edges of leaves

[mysidx]

I just noticed some of my six inch tall seedlings have soft limp edges on some of the leaves, but only on a handful of seedlings. It kind of looks like old lettuce when it gets mushy and brownish on the edges. Any thoughts of what it might be? I did use some liquid miracle grow last time I watered, which is the first time they received any nutrients. I have noticed some insects flying around my grow station which is out in the garage.