Dry/Fert burn Leaves?

I can't figure out what is going on with my fan leaves i've been flowering for 3 weeks. I have a DR120 Grow Tent with a 400W HPS Sun System 2 Enclosed Ballast Grow Light with 6 cfls the temperature in the tent are around 77-80 degrees Fahrenheit the the hps light is 5 inches away from the cola, i figured its ok because i have a can fan cooling the light by sucking the air through the light fixture and i have tempered glass so the heat from the bulb won't burn the top of the plants. But do you think maybe that is too close? When i squeeze the leaves it makes a crunching sound so im thinking maybe its heat stress or nute burn.

bump No body ever have this kind of problem?

Looks like Mag deficiency. Do your nutes have Magnesium in them? If so, what's the PH?


Add a teaspoon per gal of epson salt (Magnesium Sulfate) for a quick fix.


Edit- Agree with below post. 5 inches is crazy close. Is that a cool tube?

I let my plants get as close as 10 inches to my 400w MH in my veg room just before they go into flower without problems. I never raise or lower the light because the young plants like to be further away anyway. 5 inches seems excessive and would probably be why they feel crispy.

that light sounds a little close

Yeah, it's a cool tube. I can place my hand directly on the glass. The top leaves, being closest to the light are unaffected, it is the bottom leaves that have this going on.

Regardless, I'm almost positive it's Mag. It's one of the easiest to tell. There isn't much else that causes the distinct rust spots other then that.

Could that be from not PHing the water? I was thinking at first it might be nute burn. I'm using fox farm, all three, plus the powders. But I dont have a ph or ppm meter yet.

It could.

If you don't have the cash for a digital PH meter, go to a pet shop and get the PH drops.

I have drops that only show a PH range of 6-7.5, which is the range you are looking for wanting about 6.5. You get a lot more accuracy then trying to tell the PH of strips where you can barely tell the difference between 6 or 8 and it doesn't help any.