sea urchin black areas/lost spines

[maevepotter]

I banished this guy to a fish only tank that probably was really high on nitrates, bad decision in retrospect, but the urchin had started to eat various Lps and leathers. He seemed to get stuck behind a rock at one point, and I'm wondering if he got a heater burn maybe? He ate a ton of chaeto in there and we were feeding nori. He's been falling off things and having trouble turning over. He's still eating and moving.

I attached a flash picture to highlight the damaged areas. Any thoughts?

 

[ndrwater]

Doesn't look great. What are the parameters? How high is high concerning nitrates? Is the salinity in check?

 

[maevepotter]

I can't say, re parameters, because I broke that tank down. I'll have to test the new tank. The salinity may have also fluctuated a bit because we were topping off by hand in that tank.

 

[maevepotter]

Basically just wondering if anyone else has seen that happening to the carapace of the animal before?