Hello everyone, I am in dire need of some help. I started flowering 3 plants on February 28th, they had been in veg since January 19th. I started them in 50/50 pro mix and fox farm ocean forest. I have them in 3 gallon containers with a 1000 watt HPS setto 75% power. Starting about a week ago I started seeing these spots appear in on only one of three of my plants, within day the leaves are yellowing and dying. I have been feeding "light feeding" of general hydroponics veg nutrients the last few days thinking it was maybe a nutrient deficiency, but to no avail. I checked the Ph of my water and it's about 7. Although when I took a PH of the run off from the plant it was way down at 5. I'm assuming the problem is the PH but maybe someone has seen this issue before. Almost all the leaves are getting the early stage spots now and I can see the other plants beginning to shows signs of the same problem. I fear they will all soon die if I can't figure out the problem. If it is the PH how can one adjust PH in soil? Thank you guys very much for your time. I have attached pictures starting with early stage to late stage of my problem, thank you again.