IMO i would flush with 6.5ish water. 3 times the amount of the container. After flushing it usually takes awhile to dry out. Let it dry out so the pot is real light or the plant starts drooping a little. Then continue watering around 6.5ish. When you start feeding nutes again start off small (1/4 or 1/2 of the recommended dose) and work your way up to full strength. I think your plants are gonna appreciate that extra 150 HPS. Keep and eye on those temps when you add it. Your babies should be fine once the ph is right and that hps is put in. Good luck