oh snap. freaking AIPTASIA!?

[alix2.0]

hydroids. maybe. the picture isnt that great, but thats basically what they look like.
https://forums.saltwaterfish.com/t/164040/hydroids

 

[yosemite sam]

Yeah, that's what they sound like. They are a pain to get rid of totally, but you can try supergluing them, or using the underwater 2-part epoxy and just covering them up.