black spiny uchin question

[sansouci01]

I've had a black spiny urchin for about three months. He seems to be doing fine. Loves hanging out on the back glass. Seems that is where most of the algae is. I noticed the other day, one of his spines on the sand bed. I've read that if they start losing there spines, it could be a sign of bad water perimeters. My water quality tests good. Is it normal for them to lose spines once and a while or should I be concerned ?

 

[Holygral]

I have had one for more than 10 years and I find a spine here and there all the time.