Looks like nute burn to me,give em a pint of fresh water to flush them through,leave them for a day or so and concentrate on the top foliage cos the bottom leaves will die anyway from lack of light.Peace
you can try and flush it with a half gallon of water since its kind of small maybe??? it does look look like nute burn but sick made a good point the tips would be brown ??? so my guess it just might be you gave it too much blood meal or bone meal just light flush it see what happens .....