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?

Algae, contrary to popular belief is 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. This means that they can also produce oxygen during daylight and consume it at nights. 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 a neighbor who has a perfectly manicured lawn. Even the best-groomed lawns will occasionally get weeds (such as algae in an aquascape). These weeds must be addressed. 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. The same goes for algae control. We want to make sure you don’t see it, and that your tank looks spotless.

Why Does My Fish Tank Have So Much Algae?

Algae is caused by an imbalance of nutrients and lighting in your aquarium. This simple statement can be a little difficult to unpack, but basically, your plants need just the right amount of lighting and nutrients for optimal growth. The algae will thrive on too much light and not enough nutrients to build their cells. Algae will benefit from the additional nutrients if you give them too much nutrients and not enough light. This regulates the speed at which plants can use the nutrients. A perfectly balanced tank is not possible. Your plants will grow and you will have to prune them.

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. We have found this one-two punch strategy quite effective at greatly reducing algae to unnoticeable amounts. 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. 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)

BBA is one of the most problematic algae that people run into because not many things eat it. It grows in thick, bushy clumps, usually black or gray in color, but sometimes reddish-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. BBA can grow on many different things, so there is no single treatment.

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. It may turn reddish or clear as the algae dies, and animals might eat it. 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, try decreasing your lighting period, increasing fertilization, or decreasing iron. Siamese algae eaters, amano shrimp, molly fish, and Florida flagfish are good candidates to use as clean-up crew. 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. 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.

Because they like GSA, Nerite snails can be a good first defense. 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 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.

Blue-green algae or cyanobacteria

BGA can be photosynthetic and you may want to blackout your tank for one week. This can be difficult on 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. If the problem persists, you can repeat the treatment once more. Read our complete article to learn more about treating 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. These phytoplankton can multiply so fast that it is difficult to flush them out with large water changes. 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). Green water can be removed by blacking out the tank for at minimum one week. This can be very harmful to your plants. A UV sterilizer can be purchased, which will kill the algae in as little as 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 go back to our example where you have a green lawn with five dandelions.

It is not sensible to stop watering your grass (e.g., stopping using fertilizers or lighting) in order to eliminate a few unwanted weeds. This will likely lead to your grass dying. 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.

The Internet claims that if you do everything perfectly, your tank will never get algae, but in our experience, this is highly unlikely in the real world. Even Takashi Amano, known as the father of modern aquascaping, popularized the usage of the algae-eating amano shrimp to keep his planted tanks clean and beautiful. So, don’t be afraid to bring in the right algae eaters to help out while you’re trying to fix your lighting and nutrient balance issues. All the best with your plant-keeping endeavors!