David Wolfenden explains how to treat green bubble algae.


I have a big problem with green bubble algae in my 240 l reef tank. I added an Emerald crab on the advice of my aquatic shop, but he hasn’t shown any interest at all. Please can you help as the bubbles are getting between the polyps on my corals and they are spreading everywhere. Some of them are really big.

Dave says: There are several species of ‘bubble algae’, including those in the Valonia and Ventricaria genera. Whatever the species, bubble algae can be quite attractive in moderation, although they can, under the right conditions, overrun a tank, smothering corals in the process. The best way to tackle them is to combine nutrient export/ management with manual removal.

Firstly, ensure efficient mechanical filtration (which is regularly cleaned), aggressive skimming and ensure regular partial water changes. Increasing the frequency of syphoning can help, and review water movement to reduce dead spots where mulm and detritus can settle, as this can provide a nutrient sink, which will fuel the algae. It’s also worth considering if extra janitorial clean-up crew might help with nutrient cycling, which in turn will limit the availability of those nutrients to the algae. Another strategy is to outcompete the bubble algae for nutrients with Chaetomorpha or Caulerpa algae in a refugium.

Secondly, manual removal is going to be required. The vesicles or bubbles can often be lifted directly from the substrate they’re attached to (sometimes you’ll need to employ a pallet knife or similar tool to help) and syphoned away. It’s not the end of the world if it happens but try to avoid bursting the bubbles as far as possible as they could release spores, which can potentially recolonize elsewhere in the system. Over a few sessions, and in conjunction with nutrient limitation, the problem should go away.

Biological control is a difficult one, because not many fish or invertebrates reliably eat bubble algae. Emerald crabs, Mithraculus sculptus, are often touted as the best solution, but many specimens won’t touch bubble algae, and the crabs can cause problems themselves as they can opportunistically feed on inverts and even some fish; once they’re in they can be a challenge to remove. On that basis, watch out for tell-tell signs of nipped fish or corals.

David Wolfenden – Dave’s so knowledgeable in aquatics he used to teach it. Marines are his ‘thing’.


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