Setting up my 150 gallon tank....question re: live rock appears dead in some spots

[newreefer_59]

I have been circulating my tank for about 4 weeks now with ~150 pounds of live rock. Kept the lights off for the first 3 weeks and set them on for ~10 hour per day. They are 48" T5 lites and are very bright with 6 in total, so I have just let 2 run as it is still very bright looking in there. Question: some of the live rock appears dead in some spots. It has turned white in colour and appears dead on the top portion in particular. Does this recover eventually and can I help it? Tests run were:
Nitrite - almost nothing
Calcium - approx 500
Ammonia - .1
Magnesium - 1300
Potassium - 325
Alkalinity - approx 15 kh

Any opinion is appreciated.