I've just started viewing posts on this board, but I've been growing my own for a while, and I figured I'd put in my two cents.
You write that the day temp is around 90, that's too high for an indoor grow. You've got heat stress on your leaves. Phosphorus deficiency turns leaves purple, like this, Phosphorus Deficiency

What you need to do to cool the room is get the heat from the bulb out of the room. You've got to run that six inch tubing from the other side of the reflector, the side not in the pic, out of the growspace. The fact that it's summertime is probably your biggest problem. Indoor grows need good temp control.