What is this ? Pest ?

[willieboy240]

Hello. I broke down a friend’s aquarium. It’s been running for over 10 years. He gave me some of his live rock. I put it into my QT tank. These popped up on the glass. They don’t move and they grow like crazy. I thought acro eating flatworms but they don’t move. Plus the only coral he had was a Kenya tree, toad stool, 2 mushrooms. He had acros a long time ago but they died. Any clues or thoughts ?

 

[TnFishwater98]

Hello. I broke down a friend’s aquarium. It’s been running for over 10 years. He gave me some of his live rock. I put it into my QT tank. These popped up on the glass. They don’t move and they grow like crazy. I thought acro eating flatworms but they don’t move. Plus the only coral he had was a Kenya tree, toad stool, 2 mushrooms. He had acros a long time ago but they died. Any clues or thoughts ?

Is there a foot attached to glass? Is it bobbing in the current? Hard to tell with pic

 

[willieboy240]

Looks like there’s a foot. It’s flat. Falls off in the current a floats away. Almost looks like coralline algee but it’s brown.