Sea urchin questions

[DaJMasta]

I've had a halloween urchin in my 24G tank for a couple of months now. I never had much algae growth in the display (the tank is still a bit on the new side), so I've been feeding the urchin pieces of dried seaweed. I think I'm averaging about 2-3 pieces per week at maybe 6-8 square inches per piece as the feeding schedule, and up until two days ago he seemed to be doing just great.

Well the urchin took a very sudden turn for the worse, loosing almost all of his spines overnight, but he's not dead and I've been trying to nurse him back by putting extra food under him and checking up on him every few hours. It's been 2 days since he lost all of the spikes and he's showing reasonable activity. His body is showing more signs of distress than yesterday, but there's much more of a response from the spines he does have (on the bottom near the mouth) and he's faster to reorient himself when moved. For symptoms that seemed like a death knell, he's been continuing on like a champ. I don't know what caused the initial problem though.... none of the parameters had changed suddenly then, no ammonia, less nitrates than even a week before, though they're still around 10ppm so I'm working to bring them down. I noticed that he tried to eat a new merman's shaving brush plant I added the day before, though it's a calcareous algae, but I haven't found any information saying that would be particularly bad. There was even food in the tank from the day before when the problem occurred, so I'm baffled as to what actually happened.

Regardless, my actual question is how much do these guys eat? Was my 12-24 square inches of nori a week too little for a 2.5" or so bodied urchin? Even if supplemented with a bit of algae from the rocks/glass/wherever he finds it? I don't think water parameters or temperature was to blame, could it have been an infection?

The prognosis is somewhat grim, loosing spines quickly is a known bad sign for urchins, and today I noticed some tube feet on the sides of the body with no spines have deteriorated and there's even a bit of paleness on the outside of his body now.... but I'm trying to keep him as happy as possible. None of the tank mates should have messed with him, I specifically went a peaceful tank route, but even better nothing has tried to pick at him since the incident. Is there some kind of treatment that I can give him to help any? I haven't really seen invert treatments around because I don't suspect that we know all that well how to treat them, but should I be trying to shade him or something as well? Maybe a different kind of food?

For what it's worth, he was never one to hide much, only going into the shadows a bit during the time he was healthy. He was usually cruising around the glass and picking up frags and such to move them around.

[+Hydro]

I hope someone here has enough knowlwdge about those guys to help you. I have one and it mostly eats is coraline algae and some hair algae, so maybe the nori isn't enough nutrition for it just in the nori. Is it still eating?

[DaJMasta]

Well this morning he's still alive. I found him sort of upside down, but I think he just started to climb and rolled back, since he's got no spines on his back he's got no mobility there. I turned him over and put some more sea weed under him, and he's certainly still alive - really does look bad though.... but the closer you get to his mouth the more like a normal healthy urchin he looks like.

I don't know if he ate much of anything overnight, he certainly didn't make it through the piece placed under him, but I don't think he's had a huge appetite for at least a day or so. He definitely needed it when I first found him without spines, but since I don't think he's been eating a whole lot more than usual.

The fact that he's still alive gives me hope, but he's definitely in rough shape.