Help on first grow

This is my first grow. I grew one plant that lasted about 3 weeks prior to now, then died. I currently have a 400 watt Metal halide bulb set up running at 120v. My lighting is on 24/7, and its about 3.5 feet above the plants. I have 9-10 plants growing. Have of them are being grown in scotts potting soil and half are in miracle grow potting soil (I know several of you recommend organic soil, which will be the next grow I attempt).

Now the problem, I have one plant showing signs of brown leaves wilting, and another seems as though it is headed in the same route.

My biggest problem is the 5 week old female ak-47 I have. It started budding about 1.5 weeks ago, bud now, its original two leaves that grew when it sprouted, have died and it seems to be spreading to the larger leaves. I have attached pictures, one of my grow room and the others of my problems.

I live ina smaller area, so ph test items are hard to find. I ordered it a couple days ago, I should receive it soon.

I'm running aout of options, so any knowledgable help that would help me save my plant would be very appreciated.

Are you spraying them with something? Are you giving them nutes?

Pics 1 and 4 look like they have salt build up on the leaves and the patchy brown in the center looks like burn from spray or nutes spilled on the leaf. Could just be typical nute burn based on the brown tips.

I gave pic four fertilizer. Anything I can do to fix her? Leaves seem to be dying.