Algae in a planted tank: a common worry answered

Almost every planted tank grows algae in its first two months. People message us photos at night, sure that something has gone badly wrong. Usually it has not. Algae is a sign that light and nutrients are out of balance, and in a new tank they nearly always are.

Brown dust on the glass and leaves in the first weeks is diatoms. It wipes off easily and usually disappears on its own once the tank matures. Otocinclus catfish or nerite snails will clear it in days.

Green water, where the whole tank turns pea-green, comes from too much light, often from sun through a window. Move the tank or draw the curtain in the afternoon, cut the light to five hours and keep the tank dark for three days with a towel over it. It clears faster than you expect.

Hair algae, long green threads on plants, usually means too much light for the amount of CO2. Pull it out by twisting it on a toothbrush, shorten the light, and add more fast-growing stem plants, which take nutrients the algae would use.

The one thing we ask is not to reach for chemicals first. Most algae treatments harm shrimp and slow the plants. Bring us a photo and a water test, and we will usually solve it with a light timer and a few more plants.