How to get rid of bubble algae in a reef tank

Bubble algae is a bottle green coloured single-celled algae which forms jelly bean or round, marble-like shapes in the marine aquarium. It often starts at the base of corals but can plague if uncontrolled, blocking pumps, weir intake slots and overgrowing corals. 

Large growths can be removed by hand but there is one specific critter that reefkeepers use to deal with it. The Emerald Crab, Mithrax sculptus, grows to 2” across and comes from the Caribbean. Like most crabs, it is omnivorous but will also graze algae and importantly, Valonia spp. Bubble Algae.

Look closely and the Emerald crab has spoon-shaped pincers which it uses to grab, pierce and tear the bubbles. They are largely reef safe and the only animal prescribed to deal with Bubble Algae. They are suitable for nano reefs and large reef tanks and for bad manifestations add three or more. Sometimes also available in a reddish colour.  

Image credit By Philippe Bourjon – Don de l’auteur, CC BY-SA 3.0,

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Jeremy Gay is an author, lifelong fishkeeper, and aquatic specialist. He's a former editor of Practical Fishkeeping Magazine, UK editor at Reefbuilders, a former aquatic store manager, and has collected fish in Sri Lanka and the Amazon. He's been on tv and radio, contributed to Koi Carp and Gardeners World magazines, been a product tester, a judge, and a product developer. Jeremy is here to guide and advise you on all things tropical, pond and marine, from set-up to stocking, health, feeding to breeding, as well as solving many common fishkeeping problems along the way.

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