Entering 8th week of flowering & not sure....

The plants have been under a 1000w HPS (1.5 ft away) and are being fed a couple times a week from a 1500PPM/5.8pH mixture. The temperature in the room is between 70 to 80 degrees.

Originally the fan leaves of the plants were starting to turn yellow and I thought that was only naturally being so late into flowering but now the leaves (and the bud leaves) are starting to turn brown and dry out. This is my first grow so even though the plants should be done after this week, I do not think that is true based on how they look. Any ideas?

Cal/Mag deficiency. Did this start somewhere about early to mid flower? And I'll bet it's a Sat Dom or Sat?

Started about 2 weeks ago... I began then to add veg nutes to the flowering nutes I was giving the plants (about 1/4 of the 1500PPM) What can I do now to save them?

Looks like you burnt the shit out of them. PPMs is where i would be looking. 1500 is a lot. Just my opinion, good luck

How much longer til they finish? You can add about 1 tbsp of Epsom Salts per gal to every other watering. At this point, I doubt they'll recover, but you can let her finish out and still get a yield. If you do treat with the Epsom, watch for new growth and let me know what you see.