how to avoid algae in a fish tank

How To Control Algae in A Fish Tank

(Last Updated On: May 23, 2021)

All fish tanks experience algae growth as it’s a natural part of the aquarium ecosystem. Wherever there’s light and water, there is algae. While they have some benefits, too much is a problem, so you must keep them under control.

To control algae, make sure there’s not too much light or excess nutrients in your tank. Warm temperatures also encourage them to grow, so you’ll need to monitor your tropical fish tank for signs of growth. When algae do grow, you’ll need to remove them. You can do this by manually scraping them off or getting a multi-stage filter, which is more powerful than standard filters. Carry out frequent water changes and think about getting a UV sterilizer, killing algae and other microorganisms.

Removing algae isn’t hard, but it must be done regularly to keep conditions healthy for your plants and fish.

Is Algae Good or Bad in a Fish Tank?

Algae has several uses in an aquarium – many of which are beneficial to the tank’s ecosystem. Like plants, algae use photosynthesis to convert light and organic nutrients in the water into new algae.

However, unlike plants, they can survive in worse conditions as they’re a more simplistic lifeform. They can absorb more wavelengths of light and consume compounds that plants can’t use.

Too many algae can be a problem and signify that your tank has a chemical imbalance or too many pollutants, such as ammonia and nitrites. As described by Science Daily, an algae bloom (or algal bloom) is a rapid increase in the algae population.

They occur when the tank’s exposed to too much light or carbon dioxide and too many nutrients. It can make the water go cloudy and the fish sick. However, algae aren’t all bad and have the following benefits:

Minimizes Toxins

Along with other microorganisms, including bacteria, algae help minimize toxic nitrogen in the water. Algae also use ammonia as a food source, keeping this harmful toxin under control. Ammonia is a significant problem in fish tanks. Too much poisons fish and causes:

  • Red or cloudy eyes
  • Lethargy
  • Redness around the gills
  • Appetite loss
  • Breathing difficulties

The right amount of algae keeps ammonia and nitrites at bay, preventing them from becoming a problem within the tank.

green algae on aquarium glass

Produce Oxygen

Algae produce oxygen during the day as a by-product of photosynthesis. They consume oxygen at night, but it’s usually far less than what they make, leaving enough for the fish in the tank. Algae also reduce carbon dioxide by consuming it, keeping the tank’s conditions healthy and safe for fish.

Food for Fish

Algae is beneficial for tanks because fish and other invertebrates nibble on it, meaning it’s an excellent food source. In turn, this keeps the tank clean. In fact, several fish eat algae, getting rid of the excess and reducing the chances of an algae bloom.

According to Plant Signaling and Behavior, algae produce several compounds called metabolites. They also constitute the basis of the marine food chain, providing fish with the essential nutrients they need to survive.

How Does Algae Grow in a Fish Tank?

Algae thrive when water conditions are unbalanced. Unfortunately, getting a perfect balance of temperature, nutrients, and lighting is tricky, so algae are common in almost all fish tanks. If they’re able to get a footing, they’ll rapidly multiply, becoming a problem. The following things are what causes algae to grow:

Excessive Lighting

Light is algae’s primary energy source. Without it, algae can’t grow or bloom. However, all fish tanks need light to provide fish with oxygen, vitamin D and help plants grow. A little sunlight won’t cause the algae to grow too much but leaving the lights switched on or placing your tank in direct light causes problems.

Too Many Nutrients

Algae consume decaying debris, fish and food waste, and toxic waste. Unclean tanks that contain these things provide algae with what they need to grow and proliferate.

One of the most common food sources for algae is fish food left in the tank uneaten. It decays, providing algae with the nutrients they need to grow. That’s why you should always remove any uneaten food a few minutes after you’ve put it into the tank.

If your fish don’t eat it within five minutes, they won’t return to it later on and won’t benefit from it remaining in the tank.

Warm Water

Algae flourish in warm temperatures, so they’re most common in tropical fish tanks and tanks that use heaters. Cooling the tank isn’t possible, as it’ll affect your fish, so frequently removing it is the only way to effectively keep it under control without stressing or upsetting your fish.

What Are the Different Types of Algae?

There are several different types of algae, but the kinds most commonly found in fish tanks are:

Black Algae

Black algae, also known as black beard algae, is a type of red algae that thrives in high-phosphate environments. They more commonly appear in saltwater tanks and are usually signs that either your aquarium needs a water change or the tap contains too much phosphate.

Black beard algae are safe for fish. Most are happy to swim amongst it. However, if left unattended, they grow into a thick, bushy jungle and cover all aquarium surfaces.

White Algae

White algae in a fish tank look like a web or film that quickly spreads. They look foul and become a nuisance for your fish. White algae most commonly grow on driftwood, ornaments, and rocks, but they are rarely found on the tank.

White algae’s caused by the same things as all other algae, so improving your tank’s conditions should keep them at bay. While white algae aren’t dangerous or toxic for fish, you won’t want them to take over the tank.


Diatoms aren’t really algae, but a tiny animal called a diatom. They’re problematic for saltwater tanks, as they form slimy, gold-brown coatings on the glass and objects in the tank.

Diatoms in your aquarium can turn your tank water cloudy during an algae bloom. They thrive in aquariums with poor water quality and low light, so they’re common in new tanks.

Green Algae

Green algae are most commonly found in freshwater tanks. They contain chloroplasts and undergo photosynthesis, making food and producing oxygen. Types of green algae include:

  • Sea lettuce
  • Horsehair algae
  • Dead man’s fingers

Blue-Green Algae

Blue-green algae aren’t so much an alga as bacteria. They grow on plants and decorations, creating a film and a foul-smelling odor. You’ll also find them in the substrate and on the tank’s glass.

Brown Algae

Brown algae are some of the largest algae species. They consist of seaweed varieties and kelp in marine environments. They’re not very common in fish tanks.

How To Remove Algae from a Fish Tank

As we’ve already mentioned, removing algae isn’t tricky, but it should be something you add to your tank cleaning routine. You’ll never eradicate them completely and, as we’ve already mentioned, a little bit is actually beneficial. That being said, you can keep algae under control in the following ways:

Multi-Stage Filter

A multi-stage filter can help you remove large amounts of algae. While standard aquarium filters effectively remove chemical, biological, and mechanical waste, most struggle to keep up with algae growth, allowing them to accumulate. Choosing a more powerful filter that removes algae before they can multiply will improve the environment for your fish.

The only thing to bear in mind with a multi-stage filter is that it won’t remove algae that covers glass, decorative features, and plants, so you’ll need to tackle that separately.

Manual Scraping

Even though manual scraping takes time and effort, it is an effective algae remover. You can do it alongside a multi-stage filter to ensure all the excess algae’s removed. You can find decent aquarium algae scraper online and in aquarium stores, so they’re easy to get hold of. Don’t use a razor blade to do this, or you’ll scratch the tank and ruin it. 

Before cleaning, move your fish into a temporary replacement tank and put on some thick gloves so that your skin doesn’t come into contact with the water. Scrape the glass, ornaments, substrate, and rocks until you’ve removed all the algae. Then, thoroughly rinse everything.

And if you’re wondering how to clean algae from fish tank ornaments, you can use an algae scraper on those, too.

UV Sterilizers

A UV sterilizer is a special machine that emits UV light to kill microorganisms and is one of the most efficient and effective ways to remove algae. They don’t just kill algae, but they destroy harmful bacteria and other pathogens, contributing to an unhealthy environment. The only downside is that they can be expensive, but they’re worth the investment.

Water Changes

Partial water changes should be an essential part of your cleaning regimen. They stop toxins from building up in the tank, preventing your fish and plants from dying prematurely. Not only do water changes remove toxins, but they also eliminate algae. For example, removing 50% of the water removes 50% of the accumulated algae.

While it’s tempting to replace 100% of the water in one go, doing so removes the beneficial bacteria that have developed, making conditions dangerous. Instead, swap out:

  • Once a month, if you have a powerful filter or very few fish
  • Once every two weeks, changing about 30% at a time
  • Once a week, changing 15-20% at a time
  • Twice a week, changing 5-10% at a time.


If you’re dealing with a significant or stubborn algae bloom, you might need to use an algaecide, which is a chemical that works as an algae killer and prevents future growth by destroying or suffocating them.

However, you should only use algaecides in extreme circumstances when all other methods have failed. They could have a long-term effect on your fish and plants, so only use them a couple of times a year to prevent problems.

How To Avoid Algae in a Fish Tank

There are several things you can do to minimize the chances of algae growth naturally, including:

Reduce the Light

High-output lighting that’s on for long periods of the day causes algae to proliferate. To slow the algae’s growth, reduce the amount of lighting used for your tank or lower the intensity until the algae dissipate. If you don’t have the capability to do this, turn it off for a few more hours than usual every day.

To avoid algae altogether, make sure you don’t have your lighting on too bright or too often in the day. Eight hours a day is usually enough for plants and fish. This might take a little trial and error to get right – and don’t forget your fish need light to survive.

Control Nutrients

We’ve mentioned how algae consume excess nutrients, so try to control what’s in your tank. To do this:

  • Don’t leave rotting food in the tank.
  • Remove dead fish as soon as you see them.
  • Change the water regularly to keep the nutrients low.

Another thing worth doing is to keep testing the water to ensure it’s not experiencing spikes in ammonia in nitrites. Doing this allows you to act quickly, preventing algae from making their move and bedding in.

Add Plants

Planting healthy, fast-growing aquatic plants is a good idea, as they can fight off algae naturally, preventing you from needing to step in to clean the tank too often.

Use liquid fertilizer to strengthen them and use a fixed photoperiod of eight hours. This creates a natural, healthy ecosystem that stops algae from becoming a problem.

is algae good or bad in a fish tank?

What Are Some Algae-Eating Fish?

Another way to naturally remove algae is to add algae-eating fish into your tank. Their primary purpose is to consume excess algae, keeping them at bay. Most are compatible with other fish, so do your research and choose which one fits into your aquarium the best.

American Flagfish

American flagfish hail from Florida and are known to eat hair algae. They’re hardy and temperate, meaning they suit most aquariums. They are prone to nipping at other fish’s fins, so make sure there are enough weeds for them to clean algae off to keep them occupied.

Black Mollies

Black Mollies are easy to find in the aquarium trade and make an excellent addition to most tropical tanks. Out of all Mollies, Poecilia sphenops are the best and do a brilliant job cleaning up excess algae.


Bristlenose fish are one of the best algae-eaters for your fish tank. They don’t get too big and reach around 12.5 cm in length. They’re also hardy and easy to care for, making them a unique, interesting, and efficient addition to your fish tank. They’re also beautiful to look at.  

Garra Rufa

Also called “drab,” Garra rufa fish aren’t picky about what they eat. They suck algae off rocks and stick to the bottom of the tank in search of something to eat. Despite being known as ugly fish, they’re fascinating to look at and make an exciting addition to any fish tank.

Algae-Eating Shrimp

Algae-eating by name, algae-eating by nature. These shrimp effectively eliminate all alga types and love nothing more than eating them off plants and decorative features. Other excellent algae-eating shrimp include the japonica and amano breeds. Just be mindful about what fish you keep them with, as some will eat the shrimp.

Flying Fox

Flying fox fish are universally used for algae control – specifically, hair and brush algae. They grow to be 15 cm in length, so they’re better suited to larger aquariums where they have plenty of space to move. They have a peaceful nature but are always ravenous, so they’ll also eat leftover detritus.


Otocinclus are nano-sized catfish from South America. They’re perfect for small fish tanks with little fish. They’re well behaved and spend most of their day looking for algae to graze on. They’ll eat Amazon sword plants, though, which is something to bear in mind if you have some.

African Cichlids

African cichlids are used to constantly eating algae and are happy to spend their days grazing on whatever they can find in the tank. Malawi mbuna is an excellent choice, but members of the Labeotropheus family are the best if you want quick, fast results.


Also known as bulldog plecs, chaetostoma are found at altitude in South African streams and enjoy fast-flowing, cool water. They’re tiny dwarf fish that effectively eat algae and look great, making them an excellent addition to any fish tank.

Algae is normal in all fish tanks, so don’t worry if you discover some in yours. The problem lies when you allow them to proliferate and take over the entire tank. Not only does it look unsightly, but your fish will suffer. That’s why you must do everything you can to prevent it from growing in the first place.