Just once is several years did I see my CBS cleaning my Valentini puffer, however it refused to have anything to do with my poor ichy tang who kept going up to him, begging for a cleaning. I ran out and got a fire shrimp who was more than happy to take care of the job. My CSB occasionally gets a little cranky and territorial, but has never hurt or killed anyone in my tank, other shrimp included. Perhaps he doesn't know that they are there, hanging out in the live rock.