bubble Algae?

[Thedeacon59]

Can anyone help ID this growth on a rock in my reef tank?

 

[blowmecius]

Grape caulerpa (caulerpa racemosa).

 

[Michael Hoaster]

Yep, caulerpa racemosa, possibly the peltata variant. It should not do well in a reef tank. It needs high nutrients. When it runs out of them, it will melt down, turning white and dumping all those accumulated nutrients back into your tank. It looks like a pretty small plant, so it won't do too much damage, depending on your setup. If it gets big, that's a bigger melt down. It was great in my old planted tank. Kind of a time bomb in a reef tank.

Welcome to RC!