15 Tips To Get Rid Of Red Slime Algae (Cyanobacteria)

Every reef aficionado wants to keep their aquarium beautiful and thriving. Unfortunately, one problem that can plague reef tanks is red algae (cyanobacteria). Red slime algae is not only unsightly, but can also be harmful to fish and other marine life. This type of algae produces toxins that can poison fish and other marine life.

If you are dealing with red slime algae in your reef tank, don’t despair. The aquarium community is full of reefers who have been there and done just that. In this article, we have collected some of the best tips from experienced reefers on how to get rid of red algae.

What are red slime algae?

Before we get into how to get rid of red slime algae, it’s important to clarify that this phenomenon is actually caused by cyanobacteria. So while «red slime algae» is the most common name for this problem in reef tanks, it’s not technically accurate. The microscopic organisms that cause this problem are actually bacteria, not algae.

Cyanobacteria also come in a variety of colors, including red, green, blue, brown, and black. It is common in marine aquariums, although it can be found in both saltwater and freshwater tanks. Cyanobacteria are one of the oldest groups of bacteria on earth and are believed to be responsible for helping create the oxygen-rich atmosphere we enjoy today.

While cyanobacteria are generally considered helpful, in reef aquaria they can quickly become a nuisance. When conditions are right, cyanobacteria can reproduce very quickly and can quickly take over an aquarium. When this happens, they can crowd out other marine life and produce toxins that can harm fish and other creatures.

Causes of Red Slime Algae

There are a number of factors that can contribute to the proliferation of cyanobacteria in aquariums. We will cover some of the most common causes here.

excess nutrients

The explosive growth of cyanobacteria can often be attributed to an excess of nutrients in the water. When there are high levels of phosphate and nitrogen in the water, it can create the perfect conditions for cyanobacteria to flourish.

In reef aquariums, this is often due to overfeeding. If too much food is added to a tank, any uneaten food can build up, break down and fill the entire aquarium with nutrients. This problem is also often exacerbated by lack of maintenance: if an aquarium is not cleaned often enough, this excess nutrient will not be removed at the proper rate, leading to an outbreak of cyanobacteria.

It is also important to note that substances used to promote coral growth (such as two-part solutions and water additives) can also contribute to the problem of excess nutrients. Although these substances can be great for those who want beautiful coral, they must be used correctly. Otherwise, they can add too many nutrients to the water and cause a cyanobacterial outbreak.

intense lighting

Cyanobacteria are photosynthetic organisms, which means they need light to grow. If an aquarium is turned on for too long, or if the light is too intense, it can create the perfect conditions for cyanobacteria to flourish.

This problem is often seen in new tanks, or in cases where aquarium hobbyists have recently changed their lighting. It can also be caused by an increase in the intensity of existing lighting, such as when a new light bulb is installed.

Although aquarium plants also need light to grow, they generally don’t flourish under the same intense light conditions that cyanobacteria do. So if you find that your aquarium is being overrun by cyanobacteria, one solution may be to reduce the amount of light your aquarium receives.


Although unusual, cyan growth can sometimes be caused by hypersalinity – that is, water that is too salty. In a saltwater aquarium, hypersaline water is often due to evaporation. When aquarium water evaporates, it leaves behind salt, which can increase the overall salinity of the water.

If you find that your aquarium has high salinity levels, you can use a hydrometer to test the water. If the reading is above 1.025, then the water is hypersaline and this may be causing a cyanobacterial outbreak.

The solution to this problem is simple: simply add fresh water to the tank to reduce salinity levels. You may also need to do a partial water change to remove some of the salt from the water.

Get rid of cyanobacteria: the best tips

Now that we’ve covered some of the main causes of cyanobacteria, let’s take a look at some tips on how to get rid of them.

Note: These tips are intended to address a cyanobacteria outbreak. If you want to prevent an outbreak from happening in the first place, be sure to check out the section above for tips!

1. Check if you have too much lighting

As we mentioned earlier, the aggressive growth of cyanobacteria is often caused by too much light. If you find that your aquarium is being overrun by cyanobacteria, one solution may be to dial back the intensity of your aquarium lights. LED lights are especially good for this as they can be dimmed to prevent future blooms.

You can also try turning off the lights for a few days. This will give the cyanobacteria a chance to die, though you must be careful that your plants don’t start to suffer from lack of light. Remember that glucose is a byproduct of photosynthesis, one that your plants need to survive.

2. Maintain your tank well

The lack of water changes wreaks havoc in all aquariums, but is especially problematic in reef tanks where corals need stable water parameters. If you don’t keep up with regular water changes, the inhabitants of your aquarium will start to feel the effects: a cyanobacteria outbreak and an overgrowth of algae are just a few examples.

Cyano growth is often caused by a buildup of excess nutrients in the water. If you don’t do regular water changes, these nutrients will build up over time and wreak havoc on your tank.

If you’re already dealing with a cyanobacteria outbreak, doing a partial water change is one of the best ways to get rid of it. This will help remove some of the excess nutrients from the water and make it harder for cyanobacteria to grow.

3. Introduce a protein skimmer

Everyone knows that aquariums need filtration, but not everyone realizes the importance of protein skimmers. Protein skimmers are one of the best ways to maintain a beautiful aquarium, especially if you frequently deal with problems related to leftover food.

Food sources are one of the main ways that nutrients enter an aquarium. If you have a lot of uneaten food in your tank it will start to break down and release these nutrients into the water. A protein skimmer will help remove these leftover food particles before they have a chance to do so.

Low quality foods are especially notorious for causing problems in an aquarium. If you find that you’re constantly dealing with cyanobacteria or algal blooms, it may be time to switch to high-quality foods like Hikari or New Life Spectrum. These foods are less likely to cause problems in your aquarium and will help keep your tank clean and uncluttered.

4. Consider a phosphate reactor

As we have mentioned, one of the main causes of cyanobacteria is the accumulation of excess nutrients in the water. Phosphates are one of the main nutrients that cyanobacteria need to grow, so it’s important to keep them in check.

The best way to do this is to use a phosphate reactor. A phosphate reactor is a chamber that contains media that help remove phosphates from water. The water then passes through this chamber and the phosphate concentrations are greatly reduced.

This is an especially effective method of reducing phosphate levels in a tank and can help prevent future cyanobacterial blooms.

5. Use a reliable water source

Frequent water changes can go a long way in preventing the growth of cyanobacteria, but you will find that they are much less effective if you are using water that contains high levels of nutrients.

That’s why it’s important to use a reliable water source. If you use fresh tap water, be sure to treat it with a quality dechlorinator such as Seachem Prime. This will remove chlorine from the water and make it safe for your aquarium inhabitants.

You can also opt for RO/DI water. This is water that has been filtered to remove impurities and is ideal for use in aquariums. Above all, clean water is essential to prevent the proliferation of cyanobacteria.

6. Increase water movement

Cyanobacteria tend to grow best in standing water, so it’s important to make sure your tank has adequate water movement.

Aquarium pumps are a great way to increase water flow and can help keep your tank clean and free of cyanobacteria. The pumps can also maintain a healthy level of oxygen in the water, which is essential for fish and other aquarium inhabitants.

You can also use powerheads as a means of increasing water movement. Powerheads are small submersible pumps that can be placed in strategic locations around the tank, particularly in areas where water flow is inadequate.

7. Introduce live plants

Live plants are a great way to add beauty to your aquarium and can also help keep it clean and free of cyanobacteria.

Plants are natural filters and help remove excess nutrients from the water. This hinders the growth of cyanobacteria by eliminating one of their main food sources. Additionally, plants help increase water movement and oxygenation. This is essential to maintain a healthy environment in the aquarium.

There are many different types of live plants you can choose from, so be sure to do some research to find the best ones for your tank!

8. Properly acclimatize or cure live rock

If you’re setting up a new aquarium, it’s important to make sure your live rock is properly acclimated or cured.

Curing live rock is a process where it is allowed to sit in the aquarium for a period of time (usually around 2 weeks) so that it can release any harmful toxins it may contain. Acclimation, on the other hand, is the process of slowly introducing live rock into the aquarium over a period of time (usually around 2 hours).

Either way, it is important that you do this correctly so that your live rock does not release any toxins into the water that could cause cyan growth or worse, cause harm to your fish or other aquarium inhabitants.

9. Chemical treatments

Chemical treatments such as chemical-clean, Blue Life Red Cyano RX and Stain Remover Ultralife Red Slime can be used to remove cyanobacteria from your aquarium. However, we recommend thinking of these options as a last resort for huge cyanobacterial blooms that have not been controlled by any other means.

These treatments work by removing the active cyan bloom, but can also kill other beneficial bacteria in your tank. This can cause a mini cycle in your tank, in which ammonia and nitrite levels increase. This is why we recommend using these treatments only as a last resort, and following the manufacturer’s instructions to the end should be avoided whenever possible.

We also recommend that you remove the carbon from your filter when using these treatments, as the carbon will remove chemicals from the water before they have a chance to work.

10. Bacterial Treatments

Another alternative to chemical treatments is to use a bacterial treatment. Korallen-Zucht Ciano-Clean and Dr. Tim’s Cyanobacteria Treatment are two examples of products that can be used to treat cyanobacteria.

These treatments work by introducing beneficial bacteria to the water, which helps break down cyanobacteria and prevent them from growing. These treatments are much safer than chemical treatments and can be used more regularly without damaging the tank.

However, it is important to note that these treatments will not work immediately and it may take a few weeks for the beneficial bacteria to establish themselves in the aquarium and begin to break down the cyanobacteria.

11. Physical elimination

Physical removal is another option for treating cyanobacteria and is often the most effective method.

The best way to remove cyanobacteria is simply by sucking them out of the water with a turkey baster or some other type of syringe. You can also use a toothbrush or other type of brush to remove it from rocks and other surfaces in the tank.

Once you’ve removed as many of the cyanobacteria as possible, be sure to do a water change to remove any toxins that have been released into the water.

Prevention is the best cure

As they say, prevention is the best cure, and this is true when it comes to cyanobacteria. The best way to prevent cyanobacteria is to take steps to promote a healthy aquarium environment. This means regular water changes, maintaining proper water parameters, and avoiding overfeeding. It also means making sure your live rock is properly weathered or cured.

By following these steps, you can help ensure that your aquarium is less likely to experience a cyanobacterial bloom and that any blooms that do occur can be more easily controlled.

We hope this article has been useful to you. If you have any questions or comments, feel free to post them below. Thank you for reading!

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