Valonia (bubble algae)
Spherical green algae growing on rocks in marine aquariums. Unsightly and difficult to remove. Emerald crab is the best organic remedy.
Detailed explanation
Valonia ventricosa is one of the largest single cells in the world. Each shiny green bubble is a single giant cell filled with liquid. In the aquarium they grow on live rock and can become very annoying.
Manual removal is possible but must be done carefully. If the bubble is broken it releases spores that colonise other rocks. Better to detach the entire bubble with tweezers by grabbing it at the base and pulling it away gently. Collect with a siphon to prevent the spores from spreading.
The emerald crab (Mithraculus sculptus) is the most effective biological remedy. It actively feeds on Valonia and controls its spread. Two or three emerald crabs in an average aquarium solve the problem within weeks.
Urchins (Diadema) also eat Valonia but are less selective and can damage corals.
The causes of Valonia are linked to an excess of nutrients, especially phosphates. Keeping phosphates below 0.05 ppm reduces growth. Intense lighting encourages their proliferation.
Valonia is not toxic and does not directly damage corals. The problem is aesthetic and competitive: if it grows on a coral it can shade it and slow down its growth.
Other less common bubble algae include Ventricaria and Dictyosphaeria. The treatment is similar for all.
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