Can anyone tell me whats wrong with this?

Ok heres the deal. This is my first grow and so far everything has gone great. My plants are a little over four weeks into flowering and i am having some problems with one (white widow X chemdog) All the leaves are turning yellow and dieing started from the bottom and i thought maybe thats what they do after reading some threads on here. but now the leaves at the top are turning yellow and i have no idea how to fix it. at the rate its going all my leaves will be dead by end of flower. here are some pics not good ones but i made do. i have 2 400w lights. 1 hps+ 1 MH. Could this be caused from high ph? tested it today and it is about 7. any thoughts will help.

Guess i messed that up lol

I am also using miracle grow potting soil if that helps.

The fan leaves will naturally die as the plant matures but they should begin to die at the bottom of the plant first. Is the temperature in the room above 100 degrees? One of the pics looks like a light burn. If you put your hand under the light where the tips of the plants are and it feels warm the lights are too close.

a lot of people have trouble with mg soil late in flowering. I'm not sure what you can do, but next grow use promix.