Cladophora Algae: Identification and Control
Cladophora is a tough, branching green alga, the same genus behind the Marimo moss ball. Learn to tell it from soft hair algae and how to remove this stubborn pest.
Cladophora is one of the more dreaded nuisances in a planted tank because it is genuinely tough and clings hard to whatever it grows on. It is a genus of branching filamentous green algae in the class Ulvophyceae, and notably it is the same genus behind the popular ornamental Marimo moss ball, a colonial growth form once classified as Cladophora aegagropila (now placed in the genus Aegagropila as Aegagropila linnaei). The hobby ornamental and the pest are close relatives, which is part of why Cladophora is so persistent.
Identifying Cladophora
Cladophora appears as tough filaments or coarse green turfs, typically in areas of high light and poor flow. Its defining structural feature is that the filaments branch, unlike the simple unbranched strands of ordinary hair algae. It feels noticeably tougher and does not break apart or pull away as easily as soft filamentous algae, thanks to cell walls rich in cellulose and pectin that give it strength. Many aquarists also report a distinctive earthy or musty odour when it is crushed, and it anchors firmly to hardscape and plants via holdfast or rhizoid cells.
Why it appears
Cladophora often hitchhikes into a tank on plants or hardscape and then establishes where conditions favour it: strong light, accumulated organics and poor circulation. Unlike soft hair algae, it is a higher-level alga that will not simply be starved out by a healthy plant mass, though larger, more robust plants can help by shading it out.
Control methods
- Manual removal: physically pull and uproot it, accepting that it is persistent and usually needs repeating; remove as much of the holdfast as possible.
- Spot treatment: apply a liquid-carbon product or dab 3% hydrogen peroxide directly onto affected patches with the filter briefly off.
- Improve flow and balance: increase circulation, clear dead spots and bring light, CO2 and nutrients back into balance.
- Plant competition: encourage strong, robust plant growth to shade and crowd it.
- Severe cases: in heavy infestations, removing badly affected leaves or taking out and cleaning hardscape may be the most reliable option.