Dry, spotted, rolled leaves

Problem with leaves drying, curling, spotting. The leaves are papery and very dry, with yellow and brown spotting and curling. They easily crumble. This is my first indoor grow and I ended up with four females. One is healthy and about 3 ft tall. The other three are only 2 ft tall and have a few or a lot (depending on the plant) of these problem leaves. All are in a tent 39x39 inches under 400 watt HPS. They are in 3 gal pots filled with Miracle grow organic soil (I know now this was a mistake) and have been fertilized about once a week with Miracle grow super bloom and watered with plain water once a week. They are in day about 60 since sprouting and day about 35 of 12/12 HPS lighting. They are unknown variety from bag seed and I bought the bag about a year ago, so the seed was about a year old when planted. There were also two males, since destroyed, and a hermie moved to another location. The males and hermie did not have bad leaves, and one female did not have bad leaves. There are gnats and I have sprayed with a pesticide that is labeled to be ok to put on vegatables. I also added ladybugs. I don't see any spider mites even under the magnifying glass.
Does anyone have any idea of why 3 of the 7 have these crappy leaves? Thanks for any help.

Update: I soaked with orange oil and between that and the ladybugs the gnats are gone. I believe I overwatered causing the gnats which damaged the roots. After letting the orange oil soak dry a bit I added root stimulant. Maybe, just maybe, it will be saved. If not I'll take what unripe bud I can get and make lots of cornbread. I think baking sometimes intensifies it. I think the two males and hermie were unaffected because I ignored them and moved them away from the gnats. Got no clue about the big female-- maybe she was just tougher.
I sure wish I could take the plant to the local nursery and ask the on-staff horticulturist. He's good. Degree from A&M. But I better not.

From reading your description the first thing I thought was nute burn from the soil and nutes together. There is nothing wrong with MG soil if properly watered. Most of them have time release nutes that should last up to 2 months. Nothing wrong with MG nutes either, when used properly. You probably should have waited till you saw them looking hungry before you used any. I also wonder about the PH of your water. Most of the time nute problems come from problems with the PH. What water are you using?

The first thing I thought when I looked at the pics was heat and bugs. With mites you'll see webs, but other bugs you won't and are harder to find. A good bug spray is Azamax.

Good luck.

The first thing I thought of was that you may have 4 hermies LOL.. anyways... Im guessing PH is an issue here.. and also, that MG soil has time released nutrients in it, and they can be released if overwatered..

Thanks, Grapes and CPH. I wondered too about heat as I live in a very hot place. It's 85 outside now. I have grown outside before without much trouble but have felt paranoid lately about doing that.
This is an indoor grow and I have central air but I keep the plants in a back room and even with the AC on higher than I normally put it it gets to about 90 in there after the lights are on 3-4 hours. In future I will only try to grow indoors late Nov to early March, unless I can fund an additional AC unit and/or switch to LED lights.
I fertilized about every 6 days with MG and a watering can and used the instructions on the box. The MG soil was not the kind with the little white pellets but it did say it had nutrients. I use tap water, which I think is about 7 ph according to the water dept data. Tomorrow I will get a PH test kit and find out if that is right.
I have heard that MG soil often has gnats. If I use it again I may use a covering on the top of the soil -- maybe sand for an inch or so.
Thanks again to both of you.

Heat is a different monster when you are inside. Outside they can grow in the desert at 100+ deg, inside if you get to 90 you are pushing it. Getting as much air moving as possible in there could help. Most bagged soil comes with free gnats, the sand on top won't hurt. Sounds like you've got a good grip on things

Can you take a pic using a flash? Worried about the top that I see.