Check out the size of this bubble I took out of my tank (that's a quarter in my hand). There is one more that is larger than this, but it's behind all of my rock and I can't get to it.
I've had several that size and larger...but I'm hopeful that the new display won't have the same problem with valonia that the old one had. Nasty stuff that can be very invassive if not kept in check.