Looks like a Calcium or Phosphourus def. What are you feeding? What's the pH of the runoff? How old is it? Flowering? Info helps diagnose the specific problem
Looks like you have a couple things going on, but looks like a magnesium deficiency for those spots on the leaves the others could be a couple things that look similar. I'd start by flushing it, and you should add a calcium and magnesium supplement to your fox farm nutes. I bought MagiCal because I couldn't find CalMag local. How did you mix up the nutrients strength-wise and where you checking the PH of the nutrient solution before adding them?
Alright I'd say flush then add Calmag or MagiCal to your mute mix now. I read that most people add it to the fox farms because I guess it's lacking in it. Before you do anything just confirm your soil Ph is around 6.5. You can check it by runoff or get a soil probe. I got a probe that does temperature, moisture, Ph, and light meter for $35.
Ummm, dude, an HPS light IS an HID (high intensity discharge) light. So I assume you HAVE been spraying the plants under the HPS? If so what you've basically done is to give your plants a nasty sunburn. You might also have a deficiency of some sort. So.... answer the question. Have you been spraying the plants under HPS lighting or not?
if you're near the end of flower, that's normal from the flush, there's no nutes left so leaves will show deficiencies and die off. if that's happening during veg or early flower, it's time to hit her with calmag imo
Yea bro it's your Ph!! Had the exact same problem and then switched up my Ph and they started looking fantastic!!