What are your experiences with the Purple Short Spine Pincushion Urchin? LiveAquaria lists them as reed safe with caution. I’ve had one for months now (about 2.5-3” diameter) and it has only eaten the usual (every algae it wants including some coralline). It hasn’t touched any corals (though I don’t have many). Could it be that the only major concern with its reef compatibility is when algae is scarce?