At school, my biology teacher has set up an amazing 120 gallon in one of the study rooms, it has been up for a few years but is looking better than ever. Lots of nice corals. Anyways, tonight I was staring at the tank like I usually do and I was watching a cleaner shrimp work his way around the bubble coral and the coral spit out some purple/maroon looking stuff and it got all over the shrimp. What is this stuff? Is it a defense mechanism? I did some searching but didn't find anything.