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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. 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 with an algae scrubber sponge, 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 time to eat it unless you have an army of them). 

To help get the process started, you can also 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 razor blade (for glass tanks) or gift card (for acrylic tanks) 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

Nerite snail eating green spot algae

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. 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. Unfortunately, they replicate so quickly that you cannot 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). To get rid of green water, you can blackout the tank for at least a week, which is hard on your plants. Another option is to purchase a UV sterilizer, which will kill off the algae within two to three days.

Green water

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 deal with the weeds by pulling them out (e.g., manually removing the algae or getting a snail to eat them) and/or feeding the lawn more so that it’s healthier and the weeds won’t come back as readily.

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 detailed troubleshooting steps, see our plant nutrient deficiency article to learn which specific nutrients your plants might be missing.) 

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. Best of luck on your plant-keeping journey!

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