Cyanobacteria, also known as Red slime algae, is one of the oldest life forms on earth which dates back at least 3.5 billion years. They even had a crucial role to play in forming Earth as we know it. Scientists have identified cyanobacteria as one of the primary forms of life that introduced oxygen into our atmosphere, through photosynthesis. Without this building block of life, the sky wouldn’t be blue and humans would not exist.

Because of the presence of chlorophyll, they are also known by the name of  Blue – green algae. But only half of them are found in this shade and the rest sport blackish to blue green hues. 

Due to their evolutionary experience and general robust nature, they can also infest your saltwater aquarium and spread really fast. Though they are found in reef systems in the wild, they are very undesirable in saltwater aquariums. Cyanobacteria should be dealt with to ensure a safe environment for all the animals and plants 

The main reason for their spread in saltwater aquariums is lighting issues or nutrient problems within the tank. These are the two key ingredients that any type of algae, including Cyanobacteria, need to grow. 

So when you have an infestation of cyanobacteria in your aquarium, it is best to identify the issue early and get rid of the problem quickly. The nutrient drain and the reduction in water visibility affects all fish and coral and could negatively impact their health or even cause spread of infections due to poor water quality. 

Cyanobacteria is considered a food source for larger planktonic microbes, filter feeders and grazers. Hermit crabs love snacking on cyanobacteria. But, in most cases they are not suitable for saltwater aquariums because of their ability to spread and take over.

Below, we discuss a few effective ways you can get rid of cyanobacteria in your tank and make sure you never have to face this problem again. 


Lighting is a crucial factor in maintaining the health of the tank. Cyanobacteria require light to make their food( they are photosynthetic). If you don’t have proper lighting or have excessive sunlight hours in your saltwater aquarium, it could cause you a lot of cyanobacteria build-up in crevices. 

Depending on the tank size and inhabitants, choose the right kind of light bulb for your setup. Perform regular maintenance checks to ensure that the lighting is proper and adequate. Both low light and excessively bright tanks are magnets for pests. 

You should also try to use bulbs with different intensity and optimize spectral qualities of light in the aquarium. Especially, if you’re relying on full spectrum or color enhancing tubes for the lighting of your tank system. Use a 8 hour on 16 hour off cycle for your lights as it closely mimics most natural environments. 

Water Maintenance

Water maintenance is an essential part in making sure that your saltwater aquarium inhabitants are healthy. Marine fauna consume the tank water regularly and rely on it for oxygen and food. If the water quality is poor, it affects most mobile organisms and causes a build up of organic matter, encouraging unwanted pests. 

When you don’t pay attention to the essentials like chemical and nutrient levels, it can lead to a build up of algae in the tank. This is not pertinent cyanobacteria alone, but encourages other aggressive algae like bubble algae and red algae to take over your tank. 

You should also pay attention to the levels of dissolved organic compounds in the water as they can cause nitrates to form. Monitor the levels of Phosphates and Nitrates as they are the key chemicals that can cause an algae infestation. Phosphates are formed in saltwater tank setup through the use of unfiltered fresh water taps. They can also build up with the excessive use of aquarium products that contain high levels of phosphates in them. 

Use of RO/DI Filtered make up water and high quality salt mix are the one of the remedies for it. Also check the levels of calcium, nitrogen and phosphates in the water using a lab test to determine the best course of action for the water found in your area. 

You must also be careful when you introduce a new live rock into your saltwater setup as its curing process can also add nutrients for cyanobacteria. They could also introduce impurities to the tank and it is better to use a quarantine tank for rocks before you introduce them to your aquarium. 

You always have to keep the substrate clean, rejuvenate or change filters and perform regular water changes. 

Hermit Crabs

Hermit crabs are fun and curious creatures that use shells for protection. They have become very popular in the marine aquarium world for their character and function. They can help clean your reef tank as they feed on algae and will ensure that the substrate and crevices remain dirt free. 

Hermit crabs are usually harmless and they will squeeze into cracks and crevices in your water tank and get rid of all the cyanobacteria.The most popular species of hermit crabs for aquariums include the Dwarf Blue Leg Hermit Crab, Dwarf Red-Tip Hermit Crab, Dwarf Yellow-Tip Hermit Crabs. They are fascinating creatures that change shells and exchange them amongst each other. They are the fashionistas of the aquarium world and are excellent to observe. 

They also target some aggressive species of algae including hair and red algae and also help keep the cyanobacteria problem in check. Once you perform a thorough cleaning of your tank, introduce hermit crabs to ensure that the cyanobacteria does not return 

Water Flow

Low water flow rates in your saltwater aquarium can cause an increase in carbon dioxide which cyanobacteria feeds on. So you must always maintain medium to strong current in your tank to avoid the formation of cyanobacteria colonies.

To tackle this problem, there are multiple options. You can either add a powerhead to your tank or you can install a wavemaker and other similar surge devices which can instantly increase the water flow in your saltwater aquarium. This will help increase the efficiency of the filtration systems depending upon the size of your water tank setup. 

It is one of the easiest and most effective ways to control cyanobacteria build up in your tank. Remember, they can’t latch onto rock surfaces in high current setups. If you are prone to cyanobacteria, invest in a good current generator.  

Fluconazole Treatment

Fluconazole treatment acts as an algaecide that completely kills the excess algae in the tank. But, it is cumbersome to use and not a permanent solution. Relying on regular fluconazole treatments is an ineffective strategy as a complete fix to this problem. But, in certain scenarios, it can be very useful. 

When your tank is plagued with a lot of bubble algae (or one of the other aggressive forms), you could try a fluconazole blast. It takes some time to work but kills the excess algae caked-on rocks, corals, and filters. After a fluconazole treatment, you should consider a full tank clean (within 8-10 weeks of the treatment) After this, introduce a few above-mentioned tank cleaner to help curtail the eventual re-emergence of algae in you beautiful tank setup


Cyanobacteria is a tough problem with many different solutions. Some of them (like the fluc treatment) are instantaneous and others help control spread. A mixture of 2 or even 3 of these methods is an effective way to keep this problem at bay.