Hammer question

[Vice333]

I have had this hammer coral for about 7 months which has been doing very well. Over the last few days I have noticed that the polyps on the bottom are shriveled up and not extending. The top looks fine. I tested my water about 10 min ago, and here how it came out:

Calcium 460
ALK 8.9 (which I think is a little low)
PH 8.4
Nitrates 0ppm
Phosphates 0ppm

Its under a 20000k 400 watt radium MH (light bulb is about 8 months old so needs to be replaced)

Any Ideas?

 

[Thisseemsfishy]

Alk is ok, but can be higher. Have you added anything new lately? Changed the flow?

 

[Vice333]

No, I have done nothing different. I havent done a water change in a little while, but I have a ton of water volume and all my numbers are still fine. The tank is a 90 corner and I have a 150 gallon sump in the basement, about 60 gallons is the fuge with another 90 pounds of live rock and a bunch of cheato.