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. 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. 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. 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 can be difficult to understand this simple statement, but your plants require the right amount lighting and nutrients to grow well. 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 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.

Algae Brown Diatom

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 with an algae scrubber sponge, and many animals (like otocinclus catfish, snails, and shrimp) like to eat it. Most commonly, diatom algae is found in new tanks. It is usually caused by high levels silicates or phosphates. Diatom algae is one of the easiest to eliminate. If you wait, it will consume excess phosphates.

Brown algae

Black Beard Algae

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. 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. Some plants, such as 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. Animals may eat the dying algae if it is still clear or red. 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 cause problems because they grow quickly or are difficult to eradicate. These algae can be caused by an excess of nutrients (such as iron), too light, or a lack of nutrients (to meet the long lighting time). Therefore, you can decrease your lighting time, increase fertilization, or decrease iron. As clean-up crew, Siamese alga eaters, molly fish and Florida flagfish can be used. 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. Too much light or an insufficient amount of phosphate can lead to an outbreak. 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. The distinctive smell is something that many fish keepers recognize. 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. 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. 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. They reproduce so fast that large water changes are not possible to flush them out. Too much light (especially during the day), excess nutrients (such accidentally double-dosing fertilisers), and ammonia spikes (such as a new tank not cycled yet, or pet sitting). 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 take our example, where we have a green lawn with five dandelions.

It’s not a good idea to stop watering your lawn (e.g. stop using fertilizers and lighting) to remove a few weeds. You’ll likely end up killing your grass. 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.

Your focus should be on successfully growing lots of plants, not necessarily on eliminating algae at all costs. 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. The use of the algae-eating shrimp amano was popularized by Takashi Amano (the father of modern aquascaping). Don’t be afraid of bringing in the right algae eaters when you need them to help with your lighting and nutrient imbalance issues. All the best with your plant-keeping endeavors!