Is the bottom of you jar touching that Pyrex dish? That could be your problem. Try raising the jar with a few mason jar lid rings. The water will now be able to buffer any uneven heat before hitting your slab.
Slowly bump them up to as much light as you need. If you only have 1 light turn it on for 3-4 hours then finish lighting schedule with t5. Slowly move up.
I'm not down wit phantom 315w ballast. Keep it to the original. Phillips ballast and bulb only. They designed it, I feel like their technology is much better.
Last yield with 6 315s was 7.5 lbs of usable bud. 1.5 of larf. I know if they were my 600s the yields would have been slightly higher. But watt for watt these things rock. I'm happy with them.