tunicates are one of the only organisms commonly having a nutritional need for vanadiumColonial tunicates for sure (why the importance f clearer photos-well done). These are filter feeders and of no harm UNLESS they invade other coral in the tank. They are also known as sea squirts and often times they have very specific nutritional requirements that are not well documented depending on type. Many tunicates are misidentified as sponges. I hope these continue to do well in your system because these tunicates look amazing.
Update: Our tank has recently hit it's "ugly" phase. DKH dropped pretty fast, and we are having fun trying to figure out just how much to dose. Yay us!!! Sadly, these little dudes are no longer around for us to enjoy. Sorry for the late update!