Go to ReefTopia and get you 30-50 of the pincushions. You need a full platoon and not just a unit of them. Any less and they just take their sweet little time just to mock you. You can give them away when they mow it down in a few months... or they can stick around and keep your coralline in check. The urchins are not effective if you let your N or P rise too much... does not have to be at NSW, but cannot be too high either. If the N and P gets too high, they just really seem to slow down - if it gets really high, they will die. IMO, snails are a joke for a job like this. Fun fact, but these can live to be more than 100 years old, I guess. Other than moving around frags, they are my favorite algae eaters, are cheap at hardy.
https://reeftopia.com/collections/s...ucts/sea-urchin-pincushion-l-variegatus-4-lot