I resorted to treating my entire tank with Flux Rx (fluconazole). The recommended dose is for bryopsis. The dose that works for Valonia is 4x the bryopsis dose, and it is slow. But it works. I understand that it is an antifungal agent that works against an enzyme that is necessary for cell wall synthesis (which micro and macroalgae also need). It causes an arrest of fungal cell growth and, presumably, also causes an arrest of micro/macroalgae cell growth. I believe it is also most effective under bright lights, not bubbles that are hiding in the shadows--I speculate that it has to do with the faster build-up of the molecules that the normally functioning enzymes convert for cell wall synthesis--these molecules are meant to compromise fungal cell wall structures when not converted, so under high light where Valonia would normally grow, it becomes toxic. This is speculation only.
I have noticed that none of my corals or nems (which don't have cell walls because they are animals) or any fish or other inverts (which don't have cell walls either) were negatively effected to the point of death. I did notice a slight change of color in one of my RFAs that returned after ending treatment, but the RFA remained healthy by all appearances. A montipora digitata also seemed to stall in growth during the 6 week treatment. My macroalgae was toast (they have cell walls).
Coraline algae grew at an advanced pace while the bubble algae was dying away, so I assume it was unaffected by the Flux.
Additional notes:
1. I made sure to add an airstone in the AIO chamber to keep oxygen levels up in case there was an adverse effect on oxygenation.
2. I also regularly dosed "beneficial" bacteria in case there was new "real estate" left behind by the dying Valonia for other baddies like Dinos to establish themselves. PNS Probio to be specific.
3. I have ocean live rock in the tank, and I think that helps in many unknown ways.
4. Now I have a few bubbles that appear occasionally that I am staying on top of by manual removal and sucking out with pipette every few days. Like 1-10 bubbles at a time. I assume these are the ones that escaped treatment in the shadows and are looking for new real estate. It's much more manageable than before, knock on wood.
That's my experience. Happy to help if you choose the nuclear option.