Thank you for visiting! By the way… any links on this page that lead to products on Amazon and other stores/partners are affiliate links. Aquarium Store Depot earns a commission if you make a purchase.
Do you have algae in your fish tank? This is a problem that all aquarists deal with from time to time. In fact, algae are present in all aquariums to some extent. It can get a little out of control sometimes, but fortunately, there are ways to get your tank cleaned up and looking great again.
In this article, I’ll cover ten of the most common types of aquarium algae, and how you can prevent and get rid of algae when it becomes a problem. Let’s get started!
What Is Algae?
Algae are simple plants that do not have stems, roots, or flowers. They do not have leaves, but they also photosynthesize just like more advanced plants do.
Some of the algae that grow in aquariums are not actually true algae, but rather photosynthetic bacteria. Algae is interesting, and sometimes even beautiful, but it is usually unwelcome in our fish tanks!
Continue reading to learn more about this common aquarium villain.
Where Does Algae Come From?
Many types of algae are microscopic single-celled life forms, so they can easily find their way into aquariums from the air. Another common way for algae to enter aquariums is in the water that live fish are transported in, or on live plants. As you can tell, keeping algae out of an aquarium is not easy!
Keeping a hood over your tank, quarantining your livestock, and buying tissue culture plants are good strategies for minimizing the number of algae that comes into your aquarium.
11 Reasons Why You Have Overgrowth
This is a question that has caused much debate in the aquarium hobby.
Aquariums are like tiny ecosystems. There are incredibly complex processes at work in our tanks involving chemical, and biological processes. We don’t fully understand all the causes of algae growth, but we do know enough to manage algae quite effectively.
Algae is present in pretty much every aquarium, but what makes it grow out of control in some tanks? Let’s take a look at some of the most important causes:
1. Inadequate Equipment
While some advanced aquarists are able to maintain beautiful planted tanks with limited equipment, this usually ends in failure for most of us. Aquarium hardware can get expensive, but you definitely get what you pay for, so always invest in the best that you can afford.
Let’s take a closer look:
The role of your aquarium filter is not to physically get rid of algae, but rather to keep the nitrogen cycle running.
This process is known as biological filtration and it involves some very helpful types of bacteria that form colonies in the media of aquarium filters. The more media you have, and the finer its texture at a microscopic level, the more beneficial bacteria you can maintain.
You should always buy the best quality filter that you can afford. A small internal power filter is perfectly adequate for small low-tech, fish-only aquariums, but for heavily planted tanks, a good quality canister filter is going to be a better bet.
2. Poor water circulation
‘Dead spots’ can develop if your filter is not producing enough water flow to keep all of the water in your aquarium moving. Fish waste and other organic waste tend to accumulate in these areas, creating perfect conditions for algae to grow.
You can install a small powerhead, or even an airstone to create a gentle water flow throughout your aquarium. For tank tanks or for setups like African cichlid tanks that prefer more flow, an aquarium wave maker could make more sense.
Algae are photosynthetic organisms, which means they need light in order to grow, just like plants. The more light you have, the faster algae will grow, especially if you don’t have healthy aquatic plants to compete with them.
Aquariums without live plants should not have strong lighting, and your fish tank should never be exposed to direct sunlight.
4. Carbon Dioxide (CO2) Levels
Providing increased CO2 levels is very important for maximizing plant growth and health. Just pumping CO2 into the tank is not really enough, however. It’s very important that the amount of this gas available to the plants stays stable and consistent at a safe level. You can encourage algae growth by having too much or too little CO2 levels.
5. Unhealthy plants
Aquarium plants and algae are in competition in our aquariums. A heavily planted aquarium full of healthy, growing plants will naturally suppress the growth of algae.
This happens because plants and algae both use light, CO2, and nutrients to grow. If you’re providing these to your plants, but they aren’t growing, you can bet the algae will be happy to take advantage!
6. Aquarium water parameters
Since we know that unhealthy plants are like an invitation for algae, it’s important to make sure your aquarium water parameters are suitable for the plant species you are growing. This could apply to pH or water hardness for example.
Healthy growing plants need an adequate supply of nutrients to maintain good growth. Keep a regular dosing schedule and make sure to use aquarium fertilizers that provide all of the essential micro and macronutrients that your plants need.
7. Water Source
At the same time, high phosphates or silicates in your source water can also throw your system out of wack to the point where nuisance algae blooms are a problem. A good solution is to invest in an RO system. For those who need absolute pristine water for keeping fish like Discus, a RODI unit would be a solid investment. You should consider getting a water quality report from your city to determine the levels of your water and consider a TDS meter.
Aquarium algae tend to grow faster in aquariums that have higher water temperatures. This could be because dead plant tissues and other waste break down faster in warm water, providing increased ammonia levels.
This makes fish like Betta fish more difficult to keep in community tanks because of their temperature requirements. In general, coldwater fish tanks will have less rampant algae if all other factors are equal.
9. Aquarium Maintenance
Falling behind on your regular aquarium maintenance is one of the biggest causes of algae population growth.
Regular partial water changes are one of the best ways to limit algal growth. By changing the water, you are reducing the amount of nitrates, phosphates, and silicates in the water. You should also be sucking up physical waste particles from the substrate while performing a water change.
10. Overfeeding fish
Overfeeding is a very common, and often very serious problem for beginner fishkeepers. As uneaten fish food decays, it can release more ammonia than your beneficial bacteria can convert. This can cause rapid algal growth. Feed your fish only as much food as they can eat in a minute or two. Also, consider investing in higher quality food as budget food has been known to cause cloudy water.
11. Decaying plants
Decaying plant matter like dead leaves is just as bad as excess fish food and other organic waste. Trim your plants regularly and be sure to remove all of the trimmings from the tank.
10 Different Types
Now that you know more about what algae is, how it gets into your tank, and what causes it to grow, it’s time to learn about some of the most common algae types.
There are so many different types of aquarium algae out there that getting an accurate identification of what’s growing in your tank can be very difficult. There are some types of algae that are often seen in freshwater aquariums, however, and the following ten types are very common.
Compare these types of algae with what you see in your tank, and take note of the causes and possible treatments for each type.
1. Brown Diatom
- Causes: high ammonia, low lighting, low CO2, high silicates
- Chemical treatment: Tetra AlgeaControl, use a UV sterilizer, use RO water if your tap water contains silicates
- Brown diatom algae eaters: Otocinclus catfish, bristle nose pleco, nerite snails, Amano shrimp
Brown diatom algae is a common and pretty harmless type of aquarium algae. This type of brown algae often grows in new aquariums and goes away in time without any treatment.
Brown diatom algae thrive in water with high silicate levels, so if this type of brown algae becomes an ongoing issue, you might need to use reverse osmosis water.
2. Green Beard
- Causes: Photoperiod is too long, low CO2 levels, Low nitrates
- Chemical treatment: Hydrogen peroxide treatment, liquid carbon like flourish excel
- Green beard algae eaters: Rosy barbs, Mollies, Amano shrimp
Green beard algae look similar to green fuzz algae but grow longer and denser. This form of green algae can become a problem when you have too much light, not enough CO2, or a nutrient imbalance in your planted aquarium.
3. Black Beard (BBA)
- Causes: High water flow, fluctuating CO2 levels
- Chemical treatment: Hydrogen peroxide treatment, Apt Fix, liquid carbon like flourish excel
- Black beard algae eaters: Florida flagfish, Siamese algae eaters, Rosy barb
Black beard algae (AKA black brush algae) is probably the most feared algae form in the aquarium hobby. It actually looks kind of cool, but this stuff is really tough and is not easy to get rid of.
These algae grow attached to hardscape, substrate, equipment, and even the leaves of slow-growing plants like Anubias. Most algae eaters avoid BBA, but some fish like Siamese algae eaters and Florida flagfish can be helpful.
- Causes: Nutrient imbalances, unhealthy plant growth
- Chemical treatment: Apt Fix, Tetra AlgeaControl
- Hair algae eaters: Amano shrimp, ramshorn snails, otocinclus catfish
Hair algae are short filamentous algae that can grow on live plants. If you find this type of green algae growing on live plants in a mature aquarium, it’s a good sign that the plants are not in good health or not being fertilized correctly.
You can remove a lot of hair algae manually, but beware, it holds on tight!
5. Green Spot (GSA)
- Causes: phosphate deficiency
- Chemical treatment: Hydrogen peroxide
- Green spot algae eaters: Nerite snails, bristlenose pleco, otocinclus catfish
Green spot algae are common and harmless algae that appear as small dark green spots on the aquarium glass or on slow-growing plant leaves. Green spot algae are pretty tough, and not many animals will eat them, but zebra nerite snails can be helpful.
6. Blue-Green (BGA)
- Causes: Low-nitrate levels
- Chemical treatment: Antibiotics
- Blue-green algae eaters: Ramshorn snail
Blue-green algae are actually not algae at all. This slimy growth form is actually a form of bacteria known as cyanobacteria.
Blue-green algae are pretty easy to remove, but they will grow back if you do not figure out the cause of their growth. Blue-green algae can be harmful, and unfortunately, most algae eaters will not eat them.
7. Green Water
- Causes: Too much light, nutrient imbalance, lack of maintenance
- Chemical treatment: Use a UV filter
- Green water algae eaters: None
Green water (video reference) is caused by a bloom of microscopic algae known as phytoplankton in the water column. The easiest way to get rid of green aquarium water algae is to use a UV light filter or by blacking out the lights for a few days.
Green aquarium water algae are not harmful to your fish, but if you let them get out of control, they can block out light to your aquatic plants.
8. Green Fuzz
- Causes: Lack of CO2, nutrient imbalance
- Chemical treatment: Apt Fix
- Green fuzz algae eaters: Rosy barbs, Mollies, Amano shrimp, cherry shrimp
Green fuzz is also known as Oedogonium algae. It is a form of filamentous green algae that tends to grow on unhealthy plants. The best way to get rid of green fuzz algae is to provide your aquatic plants with adequate stable CO2 levels and balanced nutrients. The video above by Rachel O’Leary shows green fuzz algae growing in an aquarium for decor purposes.
9. Green Dust (GDA)
- Causes: Nutrient imbalance, too much light, lack of plants
- Chemical treatment: APT Fix
- Green dust algae eaters: Bristlenose pleco, otocinclus catfish, nerite snails
Green dust algae is a form of fine algae that settles on the glass and other surfaces inside your aquarium. This green algae does not attach itself firmly and can simply be wiped off without much effort.
Unfortunately, this will not solve a green dust algae problem but rather causes it to settle elsewhere.
- Causes: Ammonia spike, weak plant growth
- Chemical treatment: APT Fix
- Staghorn algae eaters: Siamese algae eaters
Staghorn algae grow in tough, grayish clumps that look quite similar to black beard algae. Staghorn algae tend to grow on the edges of plant leaves, and they can be pretty tough to get rid of!
Performing regular aquarium maintenance, dosing your aquarium plants, and trimming back old plant growth are all good ways of controlling pesky staghorn algae.
The ten common algae types in this list aren’t the only problems to watch out for. There are also some other non-algae-related growths that pop up in aquariums from time to time.
Let’s take a quick look at what they are, what causes them, and how to treat them.
Cloudy water is something that many new aquarium owners will experience. This is not algae but rather beneficial bacteria colonizing your aquarium.
They do not need any form of treatment and will clear up soon enough. If this occurs in a mature aquarium, however, it could be an indication of an increase in nutrients in the tank.
Cloudy water can also be caused by adding dusty new substrate to your aquarium, or by stirring up sediments during a water change.
If you’ve recently added new driftwood to your aquarium, there’s a good chance that a white moldy substance will begin to grow on its surface.
This is absolutely nothing to worry about and will clear up on its own in a week or two. Many aquarium fish will happily feed on this growth, but you can always scrub it off if you want it gone sooner.
Brown water is another common complaint that goes hand in hand with new driftwood. Tannins leaching out of the driftwood stain the water, almost like a teabag. This can take weeks and several water changes to clear up, but it is harmless for your fish.
Boiling new driftwood and changing the water several times before adding new driftwood to your aquarium can speed up the process.
Prevention is always better than cure when it comes to algae, but there are some effective ways of treating this common problem. Let’s take a look at some of the best treatment options for algae in freshwater aquariums.
There are some very effective chemical algae treatments available in the aquarium hobby. Some useful chemical treatments like bleach and hydrogen peroxide can even be found at your local drug store or supermarket.
Here is a list of aquarium products that can be helpful for controlling Aquarium algae:
- API Algaefix: Many algae types
- Apt Fix: Black beard algae, filamentous algae like hair algae
- Green Water Labs Algae Control: Most Algae types
- Seachem Flourish Excel: Black Beard Algae
As with any chemical product, it’s really important to follow doses carefully, and always use caution. This is especially important if you keep live animals in your aquarium.
Biological Treatments (Natural Algae Eaters)
Algae eaters are my favorite method of algae control, but they are not the final solution. Remember, prevention is better than cure, and algae eaters definitely fall into the ‘cure’ category.
That being said, algae eaters can be incredibly effective at controlling algae growth, and they are fascinating and awesome creatures in their own right too! There are many amazing freshwater algae eaters in the hobby, but here are a few of the best types:
- Otocinclus catfish
- Siamese algae eaters
- Molly fish
- Florida flagfish
- Amano shrimp
- Nerite snails
- Bristlenose pleco
Physical removal can be hard work, but it is a highly effective method of reducing the amount of algae and improving the look of your tank. An algae scraper, an old credit card, a sponge, and your fingers are all great for this task.
Unfortunately, physical removal is not going to solve the root cause of your algae growth, so you can usually expect the algae to grow back pretty fast.
Blackouts are another simple (but more time-consuming) method for decreasing algae in aquariums. The concept is simple, starve the algae of light and it will die. This technique works because your plants can survive for a few days without light but the algae really suffer.
Unfortunately, this technique will result in some leggy plant growth and it can take a few days for your plants to recover from the shock.
Note a blackout is total darkness. This is often best achieved by blocking out the glass with cardboard and covering the top of the aquarium. A black should last around 4-5 days. Your fish will survive not eating. They will typically go dormant during this time period.
Now that you know more about ten types of algae and the most common causes for their growth, let’s look at a useful thought process to help you solve algae problems before they get out of hand!
Remember, you need to identify the root cause of algae problems to make sure they don’t just keep coming back.
Go through this list to figure out where the problem might lie:
- Do you have good-quality aquarium lights with the correct spectrum for plant growth?
- Are your lights running on a timer for 6 to 8 hours per day?
- Is your tank exposed to any direct natural sunlight? Remember to avoid direct sunlight
- If you use T5 lights when was the light time you changed your lights?
- Do you have a good quality filter, with a large volume of quality filtration media?
- Is your tank cycled?
- Have you recently replaced your filter media or done anything that could have harmed the beneficial bacteria in your filter media?
- Do you have a CO2 injection system?
- Is it calibrated to maintain CO2 levels at 20-30ppm for the full period that your aquarium lights are on?
- Do you have good water circulation to spread the CO2 evenly in the water column?
- Are you fertilizing your plants regularly? Remember that some aquatic plants need water column fertilizers and some need a source of nutrients at their roots.
- Are you using fertilizers that provide the complete spectrum of macro and micronutrients that plants need?
Water temperature & Parameters
- Is your water too warm?
- Are your water parameters in the correct range for the types of plants you are growing?
- Are you performing regular water changes and using your water test kit to monitor ammonia, nitrite, and nitrate levels?
- Are you overfeeding your fish?
- Do you have too many fish?
- Are you removing all dead or dying plant parts, and using your gravel vacuum to keep the substrate clean?
- Do you have any algae eaters in your tank?
- Do they eat the kind of algae you are having problems with?
What type is growing in my fish tank?
There is a huge variety of algae species that grow in fish tanks. There is a good chance that the algae growing in your aquarium could be one of the ten types covered in this article, so run through the list and see if you can find a match.
Does this mean my tank is cycled?
Algae can occur in both cycled and uncycled aquariums. The best way to determine when your tank is cycled is to measure the ammonia, nitrite, and nitrate levels with your aquarium water test kit. You know your tank is cycled when your water reads zero parts ammonia and nitrite, but tests positive for nitrate.
What do they look like in a freshwater tank?
Algae can take all sorts of forms in fish tanks. It can be a variety of colors, including green, black, and brown algae.
It can grow as green slime, fine hair-like strands, spots, or even be quite tough and fibrous like staghorn algae. Some algae grow in the water column and can even make your water turn green.
How do you get rid of it in a fish tank?
The best way to get rid of algae is to figure out why it is growing in the first place, and then make the necessary adjustments.
As a quick fix, you can treat algae with algae removing chemicals, introduce algae eaters, or simply get rid of as much as you can by hand.
Is it harmful to a fish tank?
Most types of algae are not harmful in aquariums and fish tanks. Algae are a natural part of freshwater ecosystems, but to be fair, they don’t look very attractive in our aquariums.
Blue-green algae is one type of algae that can be toxic, and algae can block out light to aquarium plants if left to grow out of control, so in some cases, they can be harmful.
Is the green type harmful to fish?
Green algae is usually not harmful to fish. In fact, many fish species eat algae. It could be dangerous to your fish if it is left to fill up your tank and block up your filter, however.
Is green the variety good for a fish tank?
Green algae is not bad for your fish tank, it just doesn’t look too great. If it is not growing out of control and affecting your plants, it could be seen as a healthy part of your aquarium.
What is the fastest way to get rid of it in a fish tank?
A fast way to get rid of algae is a combination of manually removing as much as you can, and using a chemical treatment to kill off the rest. After that, you should perform a water change and consider adding some algae eating snails, shrimp, or fish species.
Algae are a really common headache in both freshwater and marine aquariums. Don’t lose hope if you’re struggling with algae, this is a fight you can definitely win with the right knowledge, equipment, and action plan!
Have you ever had an algae problem in your aquarium? Tell us about your experiences in the comments below!
Mark is the founder of Aquarium Store Depot. He started in the aquarium hobby at the age of 11 and along the way worked at local fish stores. He has kept freshwater tanks, ponds, and reef tanks for over 25 years. His site was created to share his knowledge and unique teaching style on a larger scale. He has worked on making aquarium and pond keeping approachable. Mark has been featured in two books about aquarium keeping – both best sellers on Amazon. Each year, he continues to help his readers and clients with knowledge, professional builds, and troubleshooting.