Hair algae in the aquarium: causes, removal and what eats it

Hair algae is green algae that grows in long, fine strands on plants, wood and rock. It usually means the light and the nutrients in the tank are out of step: too much light, too much of some nutrient such as iron, or too little fertilizer for a long lighting period. Remove the strands by hand, cut the light back, adjust the fertilizer, and add animals that graze it.

What hair algae is

Aquarium Co-Op groups hair algae with staghorn, string and thread algae as filamentous algae: the kinds that look like wet hair once you lift them out of the water. They are a problem because they grow fast, and some are hard to remove once settled.

Buce Plant describes hair algae as long green strands that spread quickly over plants and other surfaces. Algae in small amounts does no harm, but strands that cover leaves take light away from the plant.

Why it grows

The two sources give the same three causes:

• an excess of some nutrients, with iron named by both;
• too much light, in brightness or in hours;
• too little fertilizer for the length of the lighting period.

So more fertilizer can be the fix when the plants are short of food while the lights run for many hours. Aquarium Co-Op suggests decreasing the lighting period, increasing fertilization or decreasing iron, depending on which applies.

How to remove it

Buce Plant says that once hair algae has settled, it has to be removed by hand: scrub it off surfaces with a toothbrush, or pull it out with a siphon hose during a water change. Aquarium Co-Op recommends taking out large clumps with a toothbrush to help the algae eaters.

Animals that eat hair algae

Aquarium Co-Op lists Siamese algae eaters, Amano shrimp, mollies and Florida flagfish. Siamese algae eaters, Amano shrimp and flagfish also appear in the black beard algae guide, since they graze both. Animals keep regrowth down, but the cause still has to be fixed.

How to keep it from coming back

• Cut the light. Buce Plant puts the right range at 6 to 8 hours a day and no more than 10, and recommends keeping the tank out of direct sunlight.
• Look at the fertilizer. Avoid overdosing, especially iron-heavy products. If the tank gets long hours of light, Aquarium Co-Op suggests the plants may need more fertilizer rather than less. See aquarium fertilizer and root tabs for which plants feed from the water and which from the roots.
• Change water weekly. Buce Plant recommends it to stop nutrients building up.
• Keep plants growing. Healthy plants use the nutrients that algae would otherwise take. Buce Plant asks for plants to get the nutrients they need so they can outcompete algae; fast growing aquarium plants and floating plants are in the catalog.

Frequently asked questions

Is hair algae harmful to fish?

Buce Plant says algae is not harmful in most cases. The damage is to plants whose leaves get covered.

What eats hair algae?

Siamese algae eaters, Amano shrimp, mollies and Florida flagfish, according to Aquarium Co-Op.

Should I add more or less fertilizer?

It depends on the cause. Too much iron feeds hair algae, but so does a long lighting period with too little fertilizer for the plants. Compare your light hours and dosing with the causes above before changing either.