Filamentous algae

Green algae that form tufts and filaments on rocks, plants and decorations. Sign of imbalance between light and nutrients.

Detailed explanation

Filamentous algae (hair algae) are the most common aesthetic problem in aquariums. They form green tufts that stick to everything: rocks, plants, corals, decorations. There are dozens of different species under the umbrella term "filamentous".

The main cause is an imbalance between light and nutrients. Too much light, too many nutrients (nitrates, phosphates, excess iron), too long photoperiod, insufficient CO2 (in planted freshwater aquariums): all these factors favour filamentous fish.

In planted freshwater aquariums the solution is to re-establish the balance: reduce the photoperiod, increase CO2, reduce iron fertilisation, do more frequent water changes. Amano shrimps are formidable devourers of filamentous shrimp. A school of 10 Amano in a 100 litres tank can clean it up in a week.

In marine aquariums, filamentous often appear during maturation and disappear over time. Tangs and rabbits (Siganus) eat them eagerly. Diadema curls are also effective but not very selective.

Manual removal (with a toothpick they roll up like spaghetti) helps reduce biomass but does not resolve the cause. As long as favorable conditions persist, the algae grow back.

Diluted hydrogen peroxide (hydrogen peroxide) is an effective spot treatment in freshwater aquariums. It is applied directly to the algae with a syringe with the lights off. Fish tolerate the low concentrations used. Do not use in marine aquariums with corals.

Seachem's Excel (glutaraldehyde) is an algicide that works on filamentous fish in freshwater aquariums. It should be dosed with caution because sensitive plants such as Vallisneria can suffer.

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