I had the same problem and noticed a couple of things. Both my phosphate and nitrate levels had risen. I immediately added some Phosban, intesified the light over my refugium and cut back on the feedings to the tank. Within the course of 2 weeks my nitrates and phosphates were gone (at least, what I could detect of both with salifert kits) and the Valonia started dissapearing nicely. I do have a bubble here and there remaining but, they are tiny, not growing and out of direct eyesight.
BTW, I do have a Yellow Tang, Foxface and Eibli Mimic Tang in my tank. I did notice that once I cut back on the feedings, that they began to do a beter job at cleaning the rocks, glass and substrate (The Eibli was the ony one to pick up substrate).
Good luck