Help! See Urchin Eating Zoos!

I have a black spiny see urchin in my tank for a few months. He has been peacefully roaming the tank helping to keep it clean without bothering any other fish/corals....until the other day I saw him sitting on top of my zoos.



I pushed him off only to find the zoos gone where he was and bare rock left behind!!:help:



I do spot feed him see veggies every other day so I don't think he is hungry?? Or maybe I need to feed him more...or maybe its time to send him back to the LFS?



Advice?