Top buds are turning brown?

I have two gorilla glue #4 plants that are due to be done within the next 2 weeks, but I have had a constant issue of the leaves browning. Now I have come to see even some of the top buds are changing color and turning brown. I am wondering if you guys think this is a mold issue? To me it looks more like a nutrient deficiency issue and I am wondering if the low EC of my run off (around 1 most times) is causing a lack of nutrient uptake. These plants have suffered from nutrient lockout in the past and that also may be a contributing factor. The branches are all very discolored and red. These plants have been through the wringer and I am just wondering if I should cut my loses now or if they are at least worth keeping for use of edibles and hash.

Oh yeah and the middle photo is of one of the lower buds. You can see the reddish discoloration starting on the tip of the leaf, but most of it looks pretty healthy.

I'm thinking it's more likely what you are feeding them than mold.

What are you feeding them and what is the PH of the runoff?

I was using RO water and calmag but switched back to just tap water till the end of the grow. The soil I am using is roots organic. For a little while I was using grow by aurora innovations but I have not used it at all in the last few waters. I'm not sure of the runoff pH but the soil was slightly under 7. Also I used advanced nutrients big bud every other water during weeks 2-6.