As tuxedo urchins are often recommended to help with nuisance algae I want to share my experience with two of them, one blue and one red. They are in separate tanks, and I enjoy them and their sometimes weird behavior, so no regrets there. However, in one tank the urchin has arguably made the algae situation worse: As widely known, tuxedo urchins eat coralline algae. I can confirm that they do, a lot. It is not a problem for me per se, as I had more than enough covering my rocks (and back glass) entirely, which was also why I felt comfortable getting one, as I knew there would be food. I had no other algae in the tank with the red urchin, except a small spot with red gracilaria, which was rather pretty. So the urchin scraped parts of the rock clean off coralline (and ate the gracilaria), allowing green hair algae to grow on the rocks again. And it does not touch the green hair algae a bit... I am not sure what type it is, but it does not appear to be bryopsis (which they do not eat, as I know from web searches and the blue tuxedo urchin in my other tank). It is not a huge deal, but I did want to share for folks who want to buy tuxedo urchins for algae control. Mine have only eaten the "wrong" algae.