Algae in a shrimp tank

The short answer

Algae grows when a tank has plenty of light and spare nutrients. A little is a sign of a living tank, and shrimp spend much of their day picking at it and at the film around it. A lot of algae usually means the balance has tipped, and that is fixed by adjusting the tank rather than adding chemicals.

Step by step

1. Reduce the light

Shorten the lighting period, put the light on a timer and keep the tank out of direct sunlight.

2. Feed less

Feed small amounts and remove food nobody eats. Extra food becomes nutrients that algae can use.

3. Remove it by hand

Wipe glass, trim affected leaves and pull out hair algae with a toothbrush or your fingers during water changes.

4. Add plants and grazers

Healthy, fast-growing plants and a few Amano shrimp use up nutrients and graze, which gives algae less to work with.

5. Stay away from copper

Avoid algae products and medications that contain copper or are not marked shrimp safe, because they can kill shrimp.

Common kinds of algae

Brown film on glass and decor, usually diatoms, is common in a new tank and often fades as the tank matures. Green spot and green dust on the glass can be wiped away. Hair or thread algae grows in strands on plants and hardscape and is best pulled out by hand. Cloudy green water points to too much light and nutrients; shorten the light period and keep up with water changes.

Algae and shrimp safety

Many algae treatments and some fish medications are toxic to shrimp, copper above all. Read the label, and see medications and copper before you add anything. Large water changes to fight algae can stress shrimp and trigger problems such as a failed molt, so do them gently with dechlorinated water. San Diego tap water is treated with chloramine, so use a conditioner that handles it; details are on the San Diego tap water page.

Questions we get asked

Is algae bad for shrimp?

Usually not. Most common algae and the biofilm around it are food that shrimp graze on. Heavy growth is a sign that light or nutrients are out of balance, so it is worth fixing, but it is rarely the thing that harms the shrimp.

Why do I get brown algae in a new shrimp tank?

Brown film, often called diatoms, is common in new tanks. It usually fades on its own as the tank matures and plants take up more nutrients. Shrimp and snails will graze it, and you can wipe it off the glass.

Can I use an algaecide in a shrimp tank?

Be very careful. Many algae products and some medications contain copper or other ingredients that are harmful to shrimp. Check the label, and when in doubt do not add it. Fixing light, feeding and plant growth is a safer first step.

How long should the light be on for a shrimp tank?

Shrimp do not need much light. Many keepers run a moderate light for roughly 6 to 8 hours a day on a timer, and shorten it if algae is growing faster than the shrimp and plants can keep up with.

Will Amano shrimp clean up my algae?

Amano shrimp are well known for grazing algae, including some hair algae, but they will not clear a tank that has too much light or nutrients. Use them as helpers alongside better light and feeding habits, not as the only fix.

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