That is just poop bro, Nothing to worry about. And if you ever really pay attention to them. Its like they do it i dunno that word but when many things do something all at once. LOL. Because ill be seeing some of my zoos or palys do that after they might have eaten or something and then you'll see all of em doing it. That is the same type of zoa/paly. Its kind of crazy. I was scared it was dying the first time i seen it happen.