Sea Urching dying?

[DACJ]

All three urchins are tuxedo urchins if not the same from mespilia globulus? At least the biggest one is mespilia globulus, and it's only a little bigger than a toonie, the smallest tuxedo is smaller than a quarter...there seems to be a lot of film aglae on tank glass which i leave for them to eat, and no hair algae at all, some randon green small algae which I don't see them preying on...

Water quality is in measurement, all showing 0, and as the two smaller one are doing just fine, so I am not very convinced that my water had any spikes overnight...the one having spikes falling of is actually the biggest one, (less than 5 cm in diameter including the spike length) and it's the first thing that was introduced to the tank about 10 months ago...

BTW, it has came out from the centre of sand bed now, on the glass corners... let's just hope it doesn't fall again...I really don't want to kill it...
I was about to trade it in with the LFS, but it's only 8 dollar credit and I really don't want to give it away since it was my first tank specimen =D

It could be some thing in the water did you get your rock from a LFS or buy second hand get a copper test kit and do a test post results. do you skimm and what color is the skimmate you may not be pulling enough wast out of the water.

Bill