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.

Algae is bad for fish tanks

Algae, contrary to popular belief is not evil. Algae, like plants, use photosynthesis to convert light and other nutrients (such as fish waste) into algae 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 a neighbor who has a perfectly manicured lawn. Even they may get the odd weed, such as algae in an aquascape. This must be taken care of. Let’s imagine that your less-than-nice lawn has five dandelion-weeds growing to one foot in height. If you mow the lawn, then it will appear as if you have no weeds. The same goes for algae control. We want to make sure you don’t see it, and that your tank looks spotless.

Why is my fish tank so full of 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. Algae will multiply if you provide too much light but not enough nutrients. 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. 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 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.

Algae Brown Diatom

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. Diatom algae is one of the easiest to eliminate. If you wait, it will consume excess phosphates.

Algae with brown color

Black Beard Algae (BBA)

BBA is one of the most problematic algae that people run into because not many things eat it. It is a thick, bushy, clump-like algae that grows in dense, bushy clumps. They are often black or grey, but can also be 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. 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. 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. 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 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). You can reduce your lighting, increase fertilization, and 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. An outbreak can be caused by a variety of factors, including too much sunlight or an imbalance in 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)

BGA is not technically an algae type, but a cyanobacteria. It grows as a slimy coating on substrate, plants and decorations. 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.

Bluegreen 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. Repeat the treatment one more time for stubborn cases. 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. 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). You can blackout your tank for at most a week to get rid of any green water. This is very hard on the 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

Everyone assumes that you need to reduce lighting and/or nutrients to fight algae. But sometimes it is better to increase either one or both. Let’s take our example, where we 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.

It is important to focus on the growth of many plants and not on eliminating any 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. 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. All the best with your plant-keeping endeavors!