How to Fight 6 Types of Algae in Your Fish Tank

Do you dream of having a beautiful aquarium but end up constantly fighting to keep algae at bay? It’s a familiar struggle that many of us have been through, so in this article, let’s get a better understanding of the root causes of algae, the most common types found in freshwater aquariums, and how to gain the upper hand.

Are Algae Bad For Fish Tanks?

Algae are not evil, contrary to popular belief. Algae, like plants, use photosynthesis to convert light and other nutrients (such as fish waste) into algae growth. That means they also produce oxygen during the daytime and consume it at night. Algae are less complex than plants and can live in harsher environments than plants. They can absorb more light wavelengths and consume compounds that plants cannot.

Algae is actually a good thing for your aquarium’s ecosystem because many fish and invertebrates like to eat it and it helps clean the water as a form of filtration. Plus, certain algae can look attractive and make an aquarium seem more natural. Most people dislike the appearance of these algae, especially in planted aquariums, as it can block out the view and scenery in a fish tank.

The reality is that there is no such thing as a perfect planted aquarium that is 100% free of algae. Imagine that you live next to someone who maintains a beautiful lawn. Even they may get the odd weed, such as algae in an aquascape. This must be taken care of. Let’s imagine that your less-than-nice lawn has five dandelion-weeds growing to one foot in height. It will look as though there are no weeds if you mow your lawn. We want to know how to control algae in a way that is invisible and leaves the tank looking clean.

Why is my fish tank so full of algae?

Algae is caused by an imbalance of nutrients and lighting in your aquarium. It is not easy to grasp this simple fact, but plants require just the right amount light and nutrients for optimal growth. Algae will multiply if you provide too much light but not enough nutrients. The algae will thrive on the extra nutrients you provide, even if there is not enough light. Light regulates how fast plants can absorb nutrients. It is almost impossible to achieve a balanced tank. Even if everything is in order, your plants will continue growing or you will trim them to change the nutrients and lighting.

How do I get rid of algae from my fish tank?

Since you will always have some imbalance between lighting and nutrients, the goal is to get your aquarium as close to being balanced as possible, and then use an algae-eating crew to fill in the rest of the gap. This two-step strategy has been proven to be very effective in drastically reducing algae levels to undetectable levels. In the following section, we’ll be discussing the six most common types of aquarium algae with targeted tactics of dealing with them.

Brown Diatom Algae

Brown (and sometimes green) diatom looks like a dusty, flour-like substance covering your aquarium walls, substrate, and other surfaces. It is so soft that it can be easily scrubbed off with an algae sponge sponge. Many animals, including shrimp, snails, and catfish, love to eat it. Most commonly, diatom algae is found in new tanks. It is usually caused by high levels silicates or phosphates. This algae is easy to remove, as long as you give it time. The plants will naturally consume excess phosphates or silicates. Clean-up crews also love it.

Brown algae

Black Beard Algae (BBA)

BBA is one of the most problematic algae that people run into because not many things eat it. It is a thick, bushy, clump-like algae that grows in dense, bushy clumps. They are often black or grey, but can also be reddish or brownish. This algae likes to grow on driftwood, aquarium decor, and plants, and if left unchecked, it can completely engulf an aquarium in one to two years. Unfortunately, there’s a lot of different things that can contribute the growth of BBA, so there’s no one simple way to treat it.

Black beard algae

You can add Siamese algae eaters or Florida flagfish to your aquarium to get rid of the ugly look. However, the shrimp will take longer to eat unless you have a large number. Some people turn to chemical treatments, such as using liquid carbon to directly spray on the BBA for tough cases or to dose the entire aquarium’s water column for mild cases. Be aware that some plants, like the vallisneria plant, can be sensitive to liquid CO2.

Another chemical treatment is to spray the BBA-infested plant or decor with 3% hydrogen peroxide (purchased from your local drugstore) outside of water, let it sit for 5 minutes, rinse off the chemical, and put the item back in the aquarium. The dying algae turns red or clear, and animals may eat it in its weakened state. Remember that BBA is not a quick fix. It can take up to six to eight months for BBA to establish, so be prepared to wait at least that much time to get rid.

Hair Algae

In this category, we’re referring to the many types of algae that look like wet hair when you take them out of the aquarium (e.g., hair algae, staghorn algae, string algae, and thread algae). These algae can be problematic because they grow so rapidly or are hard to get rid of. They’re generally caused by an excess of certain nutrients (such as iron), too much light, or not enough nutrients (to match the long lighting period). Therefore, you can decrease your lighting time, increase fertilization, or decrease iron. Clean-up crew members include Siamese, molly, Florida flagfish, and amano shrimp. They can also be helped by brushing out large clumps manually with a toothbrush.

Hair algae

Green Spot Algae (GSA)

GSA looks like tiny, hard green spots on the aquarium walls and slower growing plants that are very difficult to clean off. An outbreak can be caused by a variety of factors, including too much sunlight or an imbalance in phosphate. Try using a glass-safe or acrylic-safe algae scraper (with the blade attachment) to remove the algae from aquarium walls.

Nerite snails are also a good first line of defense since they seem to like eating GSA. Just be aware that, while this species does not reproduce in freshwater aquariums, they will lay white eggs (similar to little sesame seeds) all over the aquarium, and some people don’t like the look.

Nerite snail eating green spot algae

Blue-Green Algae (BGA)

BGA is technically not an alga, but is a cyanobacteria. This cyanobacteria grows like a thin blanket covering the substrate, plants, decor, and other elements. Many fish keepers are able to identify the distinctive smell before the bacterial colony becomes visible. No one is 100% sure what causes BGA, but in general, improved aquarium upkeep and increased water circulation with an air stone or powerhead can help keep it away. Algae-eating algae won’t usually eat it so don’t count on them to help.

Bluegreen algae or Cyanobacteria

BGA can be photosynthetic and you may want to blackout your tank for one week. This can be difficult on plants. We recommend that you manually remove as much BGA as possible. Next, water changes should be made while vacuuming the substrate. The tank will then be treated with antibiotics. Use one packet of Maracyn (which is made of an antibiotic called erythromycin) per 10 gallons of water, and let the aquarium sit for one week before doing another water change. For stubborn cases, repeat the treatment one additional time. For more information on treating BGA, read our full article here.

Green Water

If your aquarium water looks like pea soup, you probably have green water, which is caused by a proliferation of free-floating, single-celled phytoplankton. They reproduce so fast that large water changes are not possible to flush them out. Green water can come from too much lighting (especially if the tank gets direct sunlight sometime during the day), an excess of nutrients (such as accidentally double-dosing fertilizers), or an ammonia spike (such as from a new tank that has not been cycled yet or overfeeding by a pet sitter). You can blackout your tank for at most a week to get rid of any green water. This is very hard on the plants. Another option is to purchase a UV sterilizer, which will kill off the algae within two to three days.

Green water

How to Balance Lighting and Nutrients

When it comes to fighting algae, everyone always assumes you must decrease lighting and/or nutrients, but sometimes the better course of action is to increase one or both of them. Let’s return to the example of a green lawn and five dandelions.

It doesn’t make sense to stop watering your lawn (e.g., stop using lighting and fertilizers) just to get rid of a few weeds because you’ll probably end up killing your grass too. Instead, we pull out the weeds (e.g., manual removal of the algae, or get a snail to eat them), and/or feed the lawn more often so it is healthier and won’t be as susceptible to the weeds coming back.

You should focus on growing plants and not eliminating all algae. To balance the aquarium, put your light on an outlet timer as a constant factor, and then gradually increase or decrease your nutrient levels with an all-in-one fertilizer. Do not make multiple or drastic changes all at once because it takes at least two to three weeks to see any difference in your plants and determine whether or not your actions helped balance the aquarium. For more information on how to troubleshoot your aquarium, please refer to our article on plant nutrient deficiencies.

Although the Internet says that algae will not grow in your tank if everything is done correctly, we have found this to be highly unlikely in reality. Takashi Amano, the father of modern aquascaping practices, advocated the use of the algae-eating amano shrimp for keeping his tanks clean and beautiful. You don’t have to be afraid to get the right algae eaters for your lighting and nutrient-balance problems. We wish you all the best in your plant-keeping adventure!