cola leaves dried up and dying

i posted this picture in the 'when to harvest' section, but thought i could give it a run here...

strain is master kush. this is the second grow with these genetics (phasing them out after this grow). same thing happened with the first harvest, but on a greater scale. it seemed like the plants were dying before they could mature. any ideas as to why the leaves inside the cola are drying out and dying?

ph is at 6.0 using RO water, gh 3 part, h2o2 in an ebb and flow system.
started flush 3 days ago.

How long you been flowering?

plants just hit week 8 yesterday.
on the first grow, about half of the plants were exhibiting these dried up, brittle cola fan leaves at wk 8, whereas this time around only one plant is doing it.

get rid of the h2o2 and just flush with water