I have killed the most invasive racemosa(microphysia) with H2O2.
You will need to target small spots for a couple days to achieve success.
But it does work.
I hit spot by spot over 1 1/2 months!
Killed it all in my 75g.
The calurpae you have is racmosa.
That is not bubble algae. It is caulerpa like previously stated. The raceemosa variety. Manual removal won't do it because of all the roots. I'd take it out of the tank, manually remove, and scrub and soak in H2O2.
I mixed mine with water when treating on a small scale. When doing it large scale, I don't see any other way of doing it...some large pieces could require a 5 gallon bucket to treat. That is a ton of H2O2.