How do I get rid of the algae in my aquarium tank?

Is Algae Bad for a Fish Tank?

Contrary to popular belief, algae are not evil. Like plants, they use photosynthesis to convert light and organic nutrients in the water (such as fish waste) into new algae growth. That means they also produce oxygen during the daytime and consume it at night. Unlike plants, algae are a less complex lifeform and therefore can survive in “worse” conditions than plants, meaning they can absorb more wavelengths of light and consume different compounds that plants can’t use.

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. However, most people don’t like their appearance, especially in planted tanks, since it blocks the scenery and viewing area 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 you have a neighbor with a well-groomed lawn of grass. 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 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. If you give them too much light and not enough nutrients as building blocks to grow, the algae will take advantage of the excess light and multiply. If you provide a lot of nutrients but not enough light (which regulates how fast plants can utilize the nutrients), then algae will take advantage of the extra nutrients. To make matters worse, achieving a perfectly balanced tank is nearly impossible because even if you balance everything today, your plants will continuously grow or you will prune them, thus changing the amount of nutrients and lighting they need.

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. 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. Because it’s so soft, it easily rubs off, and many animals (like otocinclus catfish, snails, and shrimp) like 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

Brown algae

Black Beard Algae (BBA)

BBA is one of the most problematic algae that people run into because not many things eat it. 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. 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 alge

Black beard algae

If you don’t like the look of the algae, you can try adding Siamese algae eaters, Florida flagfish, or amano shrimp (although the shrimp take a long to eat it unless you have an army of them). 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, 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. You can also help them by manually removing large clumps using a toothbrush.

hair algae

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.

Blue-Green Algae (BGA)

BGA is technically not a type of algae, but rather a cyanobacteria that grows like a slimy blanket coating the substrate, plants, and decor. It comes with a rather distinctive smell that many fish keepers learn to recognize before the bacterial colony is even 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 eaters typically will not eat the stuff, so don't count on their help in this case. 

Blue-green algae or cyanobacteria

Blue-green algae or cyanobacteria

Since BGA is photosynthetic, you can try to blackout the tank for a week, but this can be hard on the plants. Instead, we recommend manually removing as much of the BGA as possible, doing a water change while vacuuming the substrate, and then treating the tank 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. Repeat the treatment one more time for stubborn cases.