That algae is one touch one to beat. I had them in my tank and I tried everything including Vibrant but it didn't work. If I dipped it in hydrogen peroxide and it came back. It was a struggle for 3 years and finally I teared the tank down and started a new one with new rock and didn't bring anything from old tank over.
I have asked this same question in this forum but no one had any real solution to kill this algae. The best some one had come up with was that this is a type of bubble algae but bubble algae can be killed by Vibrant but Vibrant has no effect on this type of algae.