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? This is something that many people know well. Let’s learn more about the main causes of algae in freshwater aquariums and how to overcome them.

Algae is bad for fish tanks

Contrary to popular belief algae are not evil. Photosynthesis is the process by which algae convert light and water organic nutrients (such fish waste) to new algae growth. This means that they can also produce oxygen during daylight and consume it at nights. Algae are less complex than plants and can live in harsher environments than plants. They can absorb more light wavelengths and consume compounds that plants cannot.

Algae can be a positive thing for your aquarium’s ecosystem. It is a favorite food of many fish and other invertebrates, and helps to filter the water. 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.

There is no perfect aquarium. 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. Let’s assume your lawn is not as nice because it has five dandelion seeds that have reached one foot. If you mow the lawn, then it will appear as if you have no weeds. Similar to the above, we want you to be able to effectively control algae.

Why is my fish tank so full of algae?

Algae can be caused by an insufficient amount of nutrients or 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. 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 can I get rid algae from my fish tank?

There will always be some level of imbalance between light and nutrients. It is best to get your aquarium as balanced as possible and then employ an algae-eating crew. This is a two-step approach that has proven very effective in significantly reducing algae growth to undetectable levels. Below, we will be discussing six common types of aquarium fish algae along with specific strategies to deal with them.

Brown Diatom Algae

Diatom, sometimes brown or green, looks like a powdery, flour-like substance that covers your aquarium walls, substrate and other surfaces. Because it is so soft, you can easily rub it off with an algae scrubber sponge. This makes it a favorite food for many animals like shrimps, snails and catfish. Diatom algae is most commonly seen in newly planted tanks and is often caused by high levels of phosphates and silicates. It is the easiest algae to eliminate because it takes a while for the plants to consume the excessive phosphates and silicates. Even cleaners love to eat it.

Brown algae

Black Beard Algae

BBA is the most difficult algae to find because few things can 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 loves to grow on aquarium decorations, driftwood, and plants. It can quickly take over an aquarium in a matter of months if it isn’t controlled. BBA can grow on many different things, so there is no single treatment.

Black beard algae

If you don’t like the appearance of the algae, Siamese alga eaters, Florida flagfish or amano shrimp can be added. The shrimp are slow to eat, though, unless you have an army. Chemical treatments can be used to treat some cases. For instance, liquid carbon can be used to directly spray on the BBA or to add to the aquarium’s entire water column. Some plants, such as vallisneria, are sensitive to liquid carbon.

Another treatment is to spray the BBA infested decor or plant outside with 3% Hydrogen Peroxide (purchased from your nearest drugstore). Allow it to sit for five minutes, then rinse the chemical and return the item to the aquarium. It may turn reddish or clear as the algae dies, and animals might eat it. You should remember that BBA takes six to eight weeks to establish and can be difficult to eradicate.

Hair Algae

This category includes algae that look like hair when taken out of an aquarium. These algae can cause problems because they grow quickly or are difficult to eradicate. 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). Increase fertilization or decrease the iron level by decreasing lighting. You can use Siamese and Florida flagfish as clean-up crews. You can also manually remove large clumps 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. You can remove algae from aquarium walls using an acrylic-safe or glass safe algae scraper (with the attachment).

GSA-loving Nerite snails are a good choice for first aid. It is important to note that this species cannot reproduce in freshwater aquariums. They will however lay white eggs (similar looking to tiny sesame seeds) throughout the aquarium. This can be annoying for some people.

Nerite snail eating green spot algae

Blue-Green Algae

BGA is not technically an algae type, but a cyanobacteria. It grows as a slimy coating on substrate, plants and decorations. It comes with a rather distinctive smell that many fish keepers learn to recognize before the bacterial colony is even visible. BGA is not a common problem. However, it can be controlled by proper aquarium maintenance and better water circulation. The majority of algae-eaters won’t eat the stuff so don’t count them on it.

Blue-green alga or cyanobacteria

BGA is photosynthetic. You can try to blackout the tank, but this can cause damage 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. You will need to use one packet Maracyn (an antibiotic called erythromycin) for every 10 gallons. The aquarium should then be allowed to sit for one week before you do 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 broth, it is likely that you have green water. This is because of a proliferation single-celled, free-floating 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. 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 return to the example of a green lawn and five dandelions.

It’s not a good idea to stop watering your lawn (e.g. stop using fertilizers and lighting) to remove 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 then feed the lawn more to make it healthier so the weeds don’t return as often.

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.

Although the Internet says that algae will not grow in your tank if everything is done correctly, we have found this to be highly unlikely in reality. 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. We wish you all the best in your plant-keeping adventure!