Algae isn't a disease — it's a sign that light, CO2 and nutrients are out of balance. Identify which algae you have, fix the cause behind it, and it usually fades on its own.
Every planted tank has some algae — spores arrive on plants, fish and even the air. What turns a few spots into an outbreak is imbalance: more light than your plants can use with the CO2 and nutrients available. Scrubbing algae off without fixing that imbalance just means scrubbing again next week. Identify what you're dealing with, correct the cause, and most algae fades on its own.
Most outbreaks trace back to light that's too strong, on for too long, or both. Before anything else, put your light on a timer, cut the photoperiod to six hours for two weeks, and make sure no direct sunlight reaches the tank. Our lighting guide explains how to set intensity and duration properly once things are back under control.
Hard, round green dots on the glass and on slow-growing leaves like Anubias. It's usually linked to strong light and often to low phosphate. Scrape the glass with a blade, shade slow growers, and if a phosphate test reads low, a phosphate supplement can help. Nerite snails graze it off hard surfaces.
A soft, dusty brown coating on glass, plants and substrate, typically in the first weeks of a new tank. It's linked to silicates and an immature tank, and usually disappears on its own within a few weeks. Wipe it off, and let otocinclus and nerite snails help.
Dark, bristly tufts on leaf edges, driftwood and equipment. It clings hard and is strongly linked to unstable or insufficient CO2 and weak flow. Stabilise CO2 first, then spot-treat affected areas with a liquid carbon product at the dose on the label, and trim the worst leaves. Take care: Vallisneria, some mosses and shrimp can be sensitive to liquid carbon. Very few clean-up animals will touch mature black beard algae.
Long green strands that wrap around plants and hardscape, often in new or recently changed tanks. Twirl it out with an old toothbrush, fix the light, and add Yamato (Amano) shrimp, which are among the best hair-algae grazers in the hobby.
Pea-soup green water caused by free-floating algae, often after an ammonia spike in a new tank or with sunlight on the tank. Water changes alone rarely fix it because it regrows quickly. Either black the tank out completely for three to four days — covered, no light at all — then do a large water change, or run a UV steriliser, which kills the algae as water passes through it. Healthy plants tolerate a short blackout.
Slimy dark-green or blue-green sheets that peel off in layers, often with a musty smell. It isn't true algae but a type of bacteria, usually linked to poor flow, dead spots and built-up organic waste. Siphon it out, improve circulation, clean the substrate surface, and keep up water changes. A few days of blackout helps here too.
An imbalance between light, CO2 and nutrients — usually more light than the plants can use. Long photoperiods, direct sunlight, unstable CO2 and a young or lightly planted tank are the most common triggers.
Six to eight hours a day on a timer suits most planted tanks. During an outbreak, drop to six hours for two weeks while you fix the underlying cause.
Stabilise CO2 and improve flow first, since black beard algae is strongly linked to fluctuating CO2. Then spot-treat affected areas with a liquid carbon product at the dose on the label and trim the worst leaves. Take care with Vallisneria, some mosses and shrimp, which can be sensitive to liquid carbon.
Otocinclus catfish and nerite snails graze diatoms and soft films, and Yamato (Amano) shrimp are excellent at clearing hair algae. They help keep algae down but won't fix an outbreak caused by excess light or unstable CO2.
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