How to Get Rid of Green Hair Algae in Your Tank

Hair algae on live rock

Kristian Gravvold / Flickr / CC BY-2.0

Both freshwater and saltwater tanks can become infested by green hair algae. Although mainly an aesthetic issue, long tangles can actually entangle fish and invertebrates in your tank. Removal is not an easy process, but prevention is key to keep it from coming back. 

What Is Green Hair Algae?

Green hair algae is a type of algae that forms long strings, giving it a "hairy" appearance. It is also known as "string algae." There are many different species of green algae that can take on a hair-like appearance. 

More a nuisance than anything else, green hair algae is not toxic to fish or invertebrates. However, thick mats can cause fish and invertebrates to become entangled, keeping them from eating. For some varieties of fish with fewer scales, such as doitsu koi, hairy algae can cut into the fish's skin and cause secondary infections.

Symptoms of Green Hair Algae

There are many different types of algae that can grow in a freshwater or saltwater aquarium. The signs are fairly obvious and usually start as a small patch of green algae that starts to form longer hairs. This type of algae forms by slowly linking up individual cells into longer chains, so you may see it get longer over time. If left alone, some species of hair algae can grow several inches long!

As with all algae, they decrease the carbon dioxide in your system and add oxygen through the process of photosynthesis. However, when the lights go off, algae will start to respirate and use the oxygen in your water. If you do not have additional oxygen being added to your tank via an aerator or filter, your algae may out-compete your fish for oxygen, causing them to asphyxiate and die. This will also cause a respiratory acidosis and drop the pH of your tank. If your kH or alkalinity is too low, a sudden pH crash can also kill your fish.

Causes of Green Hair Algae

Unfortunately, no matter what kind of system you have, fish + sunlight = algae. It only takes one cell to start growing a healthy population. Even if you use a UV sterilizer on your water coming in with any new additions, you may have a cell or two stuck to a fish, coral or other invertebrate, who cannot be "sterilized" with UV light. Proper quarantine may help, but it is no guarantee.

Fish breakdown dietary protein to release ammonia in both saltwater and freshwater systems. Your biological filtration convert ammonia into nitrite and finally, nitrate. This nitrate is used as a food source by plants and algae. The more food for the algae, the more algae you can expect to have. You can remove excess nitrate by performing more frequent or increase the volume of your water changes. It is highly recommended to use a gravel siphon to remove excess food and debris from the bottom of your tank.

In saltwater tanks, coral supplements such as phosphates can also provide food for algae. If you have a saltwater tank, but no corals, switch to a non-coral saltwater mix in order to keep your levels low. If you have corals and still have a problem with high phosphates, you may have to use a combination of coral and non-coral salt mixes to keep your corals happy and your algae from growing out of control.

Lighting is another key component to algae growth. The more sunlight or artificial light on your tank, the more energy for algae to grow and proliferate. Try to keep your aquarium out of the sunlight, as this will deter algae growth and keep a more consistent temperature. If your aquarium has artificial lighting, make sure you have them set for designated day (on) and night (off) periods. You may consider decreasing your day periods and increasing your night periods if they will not affect your tank inhabitants.

Treatment of Green Hair Algae

Chemical additives and UV light may work well on cellular algae, but not hair algae. UV lights are a great idea for keeping algae levels low, since they will obliterate any roaming cells. The best way to remove hair algae from your systems is manual removal.

Use an algae scraper on the sides of your tank, making sure your equipment is specific to a glass or acrylic aquarium.For decor items, remove them from the tank during your regular cleanings and scrub them with a soft brush, such as a designated toothbrush, under hot, chlorinated water.

For live plants, you can gentle rub the algae off the leaves or perform a quick algaecide dip. For algae growing on substrate, the best method is to use a gravel siphon to turn the gravel away from the aquarium lighting. For algae growing on corals and invertebrate shells, you must be very gentle. Use a small airline suction device to gently remove algae growth. Never scrub them!

Barley bales, cubes and extracts have been shown to help deter hair algae from sticking to each other and forming strands. Although this will not affect the algae you already have, it will keep it from getting worse.

Never use chemical additives or pharmaceuticals to nuke your algae! This will create more problems and your algae will return.

How to Prevent Green Hair Algae

Prevention is the key to successfully battling algae in your tank. The following tips will keep your algae under control for both saltwater and freshwater aquariums.

Keep a close eye on your nitrate and phosphate levels. Perform proper maintenance and make sure your salt mix is appropriate for your tank inhabitants (coral vs. non-coral).

Use a UV sterilizer on your system to zap algae cells before they land. Use appropriate lighting for your inhabitants with set intervals and keep your tank out of natural sunlight. Be diligent with your cleanings and remove hair algae as soon as you notice it in your tank. Barley bales, cubes and extracts can help keep algae cells from linking up, provided they are used before the algae occurs.