Killing the unkillable?

[Doormatt]

Hmm. Not quite sure what's happening here.

The entire contents of my tank (37G with 20G sump, and 250W MH) consists of 10 blue leg hermits and 3 bits of Anthelia. One clump of Anthelia was utterly thriving yesterday, but when I came home from work, it was all gray and curled up. The other two clumps, which can't be more than 10cm away, are doing better than they were yesterday.

I know my nitrates are slighly high (10-20ish), but from what I was told, this wouldn't be a problem for this.

I'm not panicing in the slightest, if I lose these corals, it isn't a big deal at all...I'm just rather concerned that one of the hardiest corals out there (so I've heard) isn't doing too well in my tank

About the only thing I can think of is that yesterday they only had about 7 hours of light, and today they had closer to 10. The two that are doing better are in a less lighted (but not by much) area of the tank.

Any ideas?