Algae in fish tanks

(an article that describes types of algae, and how to get rid of them - natural and other ways)

Green algae

There are over 7,000 species of green algae, most of them being unicellular or filamentous freshwater species. Brackish and marine species also exist, so green algae can live in such aquariums as well.

Green algae are often a beneficial part of the ecosystem in the aquarium and should ideally not be vigorously eliminated. It can for instance serve as food for various inhabitants and help you keep the water quality stable by binding organic waste. There is however situations where you need to do something about the green algae, e.g. when it suddenly starts to grow much faster than normally.

If you wish to control green algae growth in the aquarium, you need to control light and nutrients. Green algae carry out photosynthesis and will therefore grow much faster when provided with plenty of light. Ideally place your aquarium in a spot where it receives no direct sun-light and do not let the aquarium lighting be on for more than 12 hours per day. When it comes to nutrients, it is important to carry out regular water changes and avoid over-feeding. Also consider keeping the aquarium well planted, because algae and plants will compete for the same nutrients.

A lot of aquatic creatures are fond of eating green algae and it shouldn’t be hard to find a species that suits your specific aquarium conditions. Fish is not the only alternative; there are for instance many snails that love to feast on green algae.

Last but not least, manual cleaning can be helpful when you wish to get rid of green algae that grow on aquarium glass, equipment, and so on. You need to be persistent, because the algae will soon reappear again after being removed, especially if you don’t do something about nutrients and light.

Blue green algae

Blue green algae are known under many different names, including blue-green algae, blue-green bacteria, and cyanobacteria. Blue green algae belong to the phylum Cyanobacteria in the domain Bacteria, but this special type of bacteria is capable of carrying out photosynthesis just like algae and higher plants. This is why it is commonly referred to as algae even though it is actually a type of bacteria.

Blue green algae is found in fresh-, brackish- and marine waters and is therefore capable of living in all sorts of aquaria. It doesn’t even need a body a water to survive and can for instance be found growing in soil and on moist rocks in the wild. This makes it possible for blue green algae to colonize parts of an aquarium that is not submerged, only moist. Some species live inside other organisms, e.g. protists, sponges, lichens and plants.

Blue green algae can fixate its own nitrogen and exist even in well kept aquariums, but excessive blue green algae growth is typically a sign of high levels of nitrogenous waste products in the water. Check the levels of ammonia, nitrate and nitrite, carry out regular water changes, and avoid over-feeding. Also make sure that biological and mechanical filtration is functioning properly.

In severe cases, it can be necessary to add 200 mg of erythromycin phosphate per 10 gallons of water. This should ideally be combined with vacuuming and meticulous scrubbing of glass, equipment and plants. Before you use erythromycin phosphate, keep in mind that it will affect desirable bacteria in the aquarium as well and can wreck havoc with the biological filtration. You might have to add new beneficial bacteria to the aquarium afterwards.

Brown algae

Brown algae are also known as gravel algae and silica algae. Excessive brown algae growth is usually a sign of high levels of silicates and nitrates in the water, light insufficiency and/or low levels of oxygen. Unlike many other types of algae, brown algae are therefore not combated by reducing the amount of light that reaches the aquarium. Brown algae typically grow in the form of brown patches on glass and other surfaces in the aquarium. It is especially common in newly set up aquariums, particularly in those where the substrate emits silicates. Silicates can also enter the aquarium through the tap water if it is high in silic acid.

To combat brown algae, start by testing the water to see if it is high in nitrates and/or silicates. If necessary, use silicate adsorbing resin in the filter. Carry out frequent water changes and avoid over-feeding to lower the amount of nitrates in the water. Increase lighting, vacuum carefully and wipe off all surfaces. If your tap water is the problem, you can start using RO water instead.

If your aquarium is newly set up, the problem can actually take care of itself as green algae start competing with the brown algae for nutrients. Including live plants in the set-up is recommended since they will compete as well.

Otocinclus and Plecostomus are both known to eat brown algae.

Hair algae

Just as the name suggests hair algae form long strands of “hair” in the aquarium and can become a nuisance for the inhabitants. This type of algae can grow really fast and can sometimes be visible only hours after a thorough aquarium scrub.

Excessive hair algae growth typically occurs when you allow the levels of nitrate to exceed 10 ppm in the aquarium. Check the water quality, carry out frequent water changes, and avoid over-feeding. You can for the hair algae to compete for nutrients by keeping the aquarium well planted.

Many well-known algae eaters refuse to eat hair algae, so make sure that you pick a suitable species if you wish to enlist the help of algae eaters to combat hair algae. Also keep in mind that many species only eat young hair algae. Be prepared to remove old hair algae manually.

Hair algae are typically introduced to the aquarium by piggy-backing on plants, invertebrates or equipment. It can grow slowly in the aquarium for many months without being noticed and then suddenly cause an algae explosion when the nitrates increase.

String algae

String algae is not the name of a certain genus or family; the term is used for all sorts of algae that grow in the form of strings, including so called blanket weed and pond scum. It can grow attached to a surface or cover the water’s surface.

A common remedy against string algae in ponds is to add barley, e.g. in the form of barley bales or barley extract. Be careful, because barley is not suitable for all aquariums. You also need to be patient; it can take quite a long time before any effect can be noticed. String algae can also be combated by limiting its access to light and nutrients, and by forcing it to compete with live plants in the aquarium.

Just like hair algae, string algae are known to enter the aquarium attached to new plants, invertebrates and equipment.

Source: Algae and algae control section at AC Tropical fish.