Spiny Urching Question

[SoylentGrundy]

Hello all!
I've got a 30 SW that I had a few spiny urchins in. (my wife saw them at the LFS and had to have them). So in they go and do fine for about 4 months. Then they stopped moving around as much and wasted away and finally dropped all the spines and both died within 2 weeks of each other. During this time my nitrates, nitrites, ammonia levels were zilch, pH of 8.3, dKH of 10, salinity 1.023. These figures have been constant. Any thoughts? Nothing picking on them, its an invert/macroalgae only tank as of this time (i find them more interesting than fish). Just wandering where I went wrong...
Thanx

[quarryshark]

They may not have had enough to eat. I have 4 in my 210 and they graze on algae but I also target feed them once or twice a week. I give them small pieces of nori and they scarf it up. Your water parameters sound fine. If you try them again, I would target feed them from time to time.
hope this helps.