THe problems my plants are having(PICS)

Ok guys, here are pictures of my problems. The first 2 pictures are of how my plants were about a week ago. This is a couple days after I gave them their last nute feeding. The third picture is how the biggest of my plants look now.

As you can see, the leaves are turning a nasty yellow/blackish color and are dying off. Many leaves have fallen off dead and brown already and the yellowing is progressing up the plant. There are also pictures of my other plants, where the leaves are also turning yellow at the bottom. The last picture is of my smallest plant, the mazar, which is having weird leaf curl at the top.

Im stressing about this guys, because I have tried to take such good care of these girls. A week ago they looked totally different, brilliant green leaves and always standing up perky. Now I think they are dying!

Does anyone know what is happening here? Can I save these plants? I really hope they aren't done for, that would be pretty heartbreaking. Is this severe nute burn? Mold?

I flushed the big plant with the really bad leaves(pic 3) today with 10 gallons of water. I hope if it is nute burn this will help it. It was standing up a little bit more. Any help is greatly appreciated!

PS: It has also been ESTREMELY hot around here, about 90-100 everyday, and they are in a greenhouse. I added a fan yesterday but before this, it was always extremely humid inside the greenhouse. Any ideas as to my problems?

So what do you guys think? Could the large blackening at the tips, yellowing of the leaf, and the progression up the plant be from acidic soil? Would that cause that?

ouch the curling on the top part of the plant is heat stress and it looks like a number of thing maybe the nuts in the soil or the water .do you ppm meter your nutrients when you feed its most likely nuts but dont take my word for it heres some info http://www.marijuana-seeds.net/Thanks-ThankYou.htm

First off, I'd say 90-100 temps is too hot to have them out in a greenhouse, they are definitely not going to do well in those conditions. It looks like they were doing great before, so unless you changed something I'd say it's the heat.

What nutrients/soil are you using? What is your water like, did the pH possibly shift?

Im using fox farm big bloom and grow big nutes. I thought it was only the one plant that was having the problems, I thought I had over fertilized it cause it happened after the first day that I gave them full dose of nutrients rather than half. Ive flushed them with PHed water, about 6.0 and it looks several have this yellowing and black curling of the tips. I attached a photo of some of the leaves that fell off today. I looked under and did see one small spider looking bug with a small web. Could all this yellowing be caused by spiders mites, or acidic soil, or over nute burn? Im just really confused on what to do, I was told to add some lime to the soil and that this could help the yellowing.

Clould it also be that I haven't fed them any nutrients in over a week and a half?

FF soil with a full strength feeding, yeah that could be a nute burn. Hopefully they respond well to the flush. The damaged stuff will not come back, but it should hopefully not spread. This isn't from spider mites, and FF soil isn't known to have pH issues, and your water seems fine, since it happened right after upping nutrients I'd guess that's what it was. Good Luck!

Well, the burn is still spreading up the plant. Leaves are turning more yellow all the time and getting crazy black about 3 quarters of the way out on the leaf to the tip. I just dont understand how one overdosing of nutes could do this. Pretty much all of my plants are developing this now, yellowing and blackening on the bottom leaves, then they crisp up and die. Im kind of at a loss for what to do here. Going to see if I can find some dolomite lime, flush them with water in the 7-8 ph range, then give them a tiny bit of nutes to see if they pick up. I really hope I didn't just kill my plants.

Sorry, man. I am at a loss. Have you read through the stickies in the MJ Plant problem forum? If you flushed and still haven't fed, it must be pH or deficiency, but your pH is good, and this started when you were using nutes. Hope you can save 'em.

Oh yeah, I was just reading another post and they were talking about the chlorine in the water. Do you let it sit before watering to dissipate the Cl?

iTHINK your plants are choosing to about the leaves that get the least light

Yup I let it sit atleast 24 hrs or more to get the chlorine out. I think the soil might be getting acidic though, because before I added the fan to the greenhouse, I would go 4-5 days without watering, and on the 5th day the soil would still be moist. This could make my soil acidic right?