Drooping and Yellowing in Week 3 Flower

I need help! i am in week 3 of flower (hydro) and all of a sudden my plants are way droopy do have a small mite problem but the ends of some of the leaves are turning dark and getting all wimpy. My nutrients are around 1095, ive taken them down to that from around 1200ppm over the past res changes. i Ph between res changes and just started topping off with phd water, i will post pics later when i can get in my room . could it be root rot? also they are turning yellow, and a lot of them have lost their nice green color towards the bottom of the plants​