Nute Burn or Sun Burn(pics and details)

I'm getting a little but of burn of some sort on my leaves. I've just recently lowered my light, and upped my nutes. I'm using a 400w hps cooltube(not currently being cooled very well) on 12/12 which is about 10-12" from the top of the plant. I'm using GH's three part mix, at about 1100ppm, just up from 1000ppm, not a big change. It's getting up to about 90 farenheit during the "day" and 65-70 at "night". I'm 4 weeks into flowering.

Here are pics:

This one's on my 'bright' setting on my phone, so the color's off.


And in true color, bit a little washed out:


Only a few leaves are like this. Any help would be greatly appreciated. Let me know or check out my journal if you need any more info or pics. https://www.rollitup.org/grow-journals/121144-my-first-grow-6.html

Thanks.

kinda looks like either foliar feed burn or it could be heat stress...

I'm not foliar feeding. I really don't want it to be heat stress since that's going to be the hardest for me to fix... but you're probably right.

it could be the plant taking most of the nutes for the buds, instead of the leaves..most plants i've seen that are flowering have leaf edges like that...

sorry dinky... wrong. deficiency looks different. im almost positive heat stress and if hes thinking the same thing.... probably is =x

dinkydigger it could be the plant taking most of the nutes for the buds, instead of the leaves..most plants i've seen that are flowering have leaf edges like that...

Yeah, some of my lower leaves are turning yellow and falling off, which I'm pretty sure is what you're talking about, but these are different.

xxtoadxx sorry dinky... wrong. deficiency looks different. im almost positive heat stress and if hes thinking the same thing.... probably is =x

I know it should be cooler in there anyway, so I suppose it's time for me to quit procrastinating and get my ventilation issue taken care of. Even if the heat's not the problem(and I'm becoming more and more sure it is), it's something I need to do anyway.

Thanks for the help guys. More input's always appreciated though, if anyone else has an opinion.

I would say it is nute burn from your increase in nutes recently, but the heat can also cause it because 90F is quite high. So I would get a fan on them if you don't already to make sure the plants are atleast a few degrees cooler than the reading. And if that doesn't help then I would assume nute burn.

If it is nute burn... that's good. I use a reservoir, and I only refill it about once a week, so the nutes get slowly weaker during that time... so I guess next time I'll just do a little weaker. I do have a fan on it, but the whole thing's in a pretty confined space. Problem, I think, is the venting. I have the air going through the cool tube, through 6" venting, into my 6" 250cfm fan, and then it directly narrows down to a 4" tube and filter. Almost all of the air bounces right back out where the tube narrows... so I'm hoping that just by having a length of 6" before the filter instead of the 4", it'll fix my air flow problem... If that doesn't help, I'll just have to start over with my vent. But 6" ducting is 4x the price of 4" ducting, which is what's been making me avoid doing it. Either way, if it's nute burn or heat stroke... how much do you think it's going to impact my harvest? Is it horrible, or just a minor glitch?

I think this won't affect it much if at all. I think if you tackle it right now you can completely reverse it. Just experiment a bit and see if you can find out exactly what it is.

Cool guys, thanks. I'll try to get the heat down and let ya know how it turns out.