How to Fight 6 Types of Algae in Your Fish Tank

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.


Is Algae Bad for a Fish Tank?

Contrary to popular belief, algae are not evil. They use photosynthesis, which is similar to plants, to convert light and organic nutrients from water (such a fish waste) into new growth. That means they also produce oxygen during the daytime and consume it at night. Algae, unlike plants, are simpler life forms and can survive in less complicated conditions than plants. This means that they can absorb more wavelengths from the sun and consume other compounds that plants can’t.

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 will get the occasional weed (like algae in an aquascape) that must be dealt with. Now let’s suppose your not-as-nice lawn has five dandelion weeds that have grown to one foot tall. If you mow the lawn, then it will appear as if you have no weeds. In the same way, we want to learn how to appropriately control algae so that you can’t see it and the tank looks like practically spotless.

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 in 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. Diatom algae is most commonly seen in newly planted tanks and is often caused by high levels of phosphates and silicates. It’s one of the simplest algae to get rid of because if you just give it some time, the plants will naturally consume the excess phosphates and silicates, and clean-up crews love to feed on it.

Brown algae

Black Beard Algae

BBA is one the most troublesome algae because it is not eaten by many animals. As per its name, it grows in very thick, bushy clumps that are usually black or grey in color (but sometimes 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. There are many things that can cause BBA to grow, so it is not possible to just treat one thing.

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. Just be careful because certain plants like vallisneria are sensitive to liquid carbon.

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. Just remember that there are no quick fixes – BBA can take six to eight months to get established, so expect it to take at least that long to get rid of.

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. You can also help them by manually removing large clumps using 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. A lot of things can cause an outbreak, such as too much light or an imbalance of 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 is technically not a type of algae, but rather a cyanobacteria that grows like a slimy blanket coating the substrate, plants, and decor. 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. The majority of algae-eaters won’t eat the stuff so don’t count them on it.

Blue-green algae or cyanobacteria

BGA is photosynthetic so you can blackout the tank for up to a week. However, this can be harmful to the plants. Instead, we recommend manually removing as many BGA as you can, performing a water change, vacuuming the substrate, then treating the tank using 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. You can read the full article on how to treat BGA.

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). To get rid of green water, you can blackout the tank for at least a week, which is hard on your plants. You can also buy a UV sterilizer that will kill all the algae within two-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 go back to our example where you have a green lawn with 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 remove the weeds manually or use a snail for their removal. We also feed the lawn more to make it healthier so they don’t return as often.

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. Don’t be afraid of bringing in the right algae eaters when you need them to help with your lighting and nutrient imbalance issues. Best of luck on your plant-keeping journey!