Valonia often refereed to as bubble algae is certainly rated high on the aggravation scale. Valonia is said to be the largest single cell organism in the world. The growing ball has no cell wall or internal divisions of any kind. In fact reproduction comes in the form of a brood stock with this algae. Hundred to thousand od offspring form inside the bubble when it reaches maturity, and when the cell walls ar torn they are released into the aquaria to settle and form new colonies.
Unfortunately with the right conditions this species will multiple at an alarming rate and quickly overrun and aquarium. One problematic aspect of Valonia is that if growing near a coral, the tissue on the coral will recede and allow the Valonia to overtake the skeleton. A critical aspect of controlling Valonia in your system is controlling the amount of free nutrient in the system. Valonia under normal circumstances should remain under control with the occasional bubble here and there.
In high nutrient systems this algae will take advantage of the opportunity to reproduce. In maintaining a reef and balancing feeding corals and fish you will have to consider the potential of the Valonia and other nuisance algae’s if they have been introduced to your closed reef system. Removal of the Valonia seems to be a laborus, and is. Although there have been reports of numerous fish and inverts that have appeared to eat this pests there are really no biological means of effective control. While I have owned some of these species I have only observed a small nibble here and there as to if sample the food. From my experience as stated previously the best control is prevention through nutrient control.
If however you find yourself in the midst of a breakout, you may have to remove the spherical bubbles manually with pointy nose pliers or tweezers. Over the past 7 years I have run into two situations where I had to completely disassemble my reef system taking the rock out, and scraping the Valonia off rock by rock. In those circumstances I was not running a protein skimmer, and was feeding heavily attempting to promote growth.