Please Help

I have dos si dos in 4x4 tent
Medium is promix in 3 gal pots
Using fox farm line of nutes at half strength
Week 4 of flower and im getting bad rust spots and curling up.Fed calmag every feeding and even tried Epsom salt it started on a few leaves and has spread to entire plants. Don't know what else to try.
600 watt full spec HID

My opinion is extreme calcium toxicity.

You're cal-magging them to death.

I now think the same. What is my fix flush ?

No, just resume normal watering and feeding minus the cal mag and probably epsom salts. Don't swing things the other way to correct, it causes more issues.

take a photo under 3500k so i can see the spots

Give them plain water 1 time around, let them almost dry out then feed just base nutrients at half strength and see what happens. This looks like a mixture of heat stress and nutrient burn.

With HPS you want to keep air temps below 80 °F and make sure the light is at least 18-24 inches from the top of the plants to prevent burning/bleaching and light stress.

Fox Farms Nutrients are notorious for burning weed plants. Worst beginner fertilizer imo.