Bubble algae (Valonia spp.) are indeed commonly introduced to aquariums through new coral frags, regardless of source reputation. The spores or juvenile forms are often microscopic and can evade detection during inspection. While coral dips are effective at removing pests such as flatworms or some protozoans, they are generally less effective at eliminating bubble algae, as the algae can survive a dip or may already be attached in a form resistant to quick removal.
Physical removal remains the primary control method. Care must be taken to extract the bubbles intact to prevent spore dispersal, which could exacerbate the problem. Additionally, biological controls such as certain emerald crabs (Mithraculus sculptus) have shown some effectiveness in managing bubble algae populations, but their results can vary and are not guaranteed. The best preventative measure is a combination of careful manual inspection, regular tank maintenance, and, where feasible, quarantining new arrivals before introduction to the main system.