leaves have brown spots

Im new to this forum. I'm 4 weeks into flowering and this problem just started a few days ago. I have six blue sugar plants and so far its only effecting one. plants r under 2 600w hps, in 5 gallon buckets with miracle grow soil. currently feeding them once a week
with miracle grow bloom formula 15-30-15. exhaust is always on and so is the box fan. temp is usually 82 miday. ph is 6.5 to 6.8. If anybody can help me identify this it would be greatly appreciated thanx

82 degrees isn't horrible, but try to lower it a couple of degrees, dont use miracle grow... its just not good for pot. it's too hot, and along with miracle grow nutrients too, id say its nutrient burn for sure. go to your hydro store and get real nutrients for pot, look at humboldt nutrients or fox farm, i use fox farm and its good stuff. go ahead and give your plants a good ol flushing and take it easy on the nutes, the brown spots wont go away, they may get a little worse until they recover from the flush. but if they proceed to get worse then i guess im wrong and you have a deficiency. hope this helps

I have never had any problems before this. The other 5 r doing great. Im definately gonna be running to the hydro store here shortly. Ive also noticed some gnats in the flowering room could they cause this? Thanx for the info. I also used superthrive and rapid start from general hydro.

It seems to be a mag cal deficiency. I also flushed the plant cause it was up to 1500 ppm, after the flush it was down to about a 1000 ppm. Also probably has a slight n deficiency. Ill see what happens in the next few days

nothing to add, 50th post.