7 Questions for an Overview of Aquarium Algae

Depending on who you ask, aquarium algae are necessary to the health of your fish or a sign that the tank is in jeopardy. We’re going to address some of the most common questions people have about aquarium algae before answering them in detail.

What is algae and what does it do?

The green algae in fish tanks are single celled plants that multiply in the tank if uncontrolled. Their scientific name is chlorophytes.

While rain forests are called the lungs of the world, in reality, it is the three quarters of the planet covered in water and filled with algae like this that creates and maintains our oxygen atmosphere. Algae are found in saltwater and fresh water, and it is found in fresh water and salt water tanks, too

The algae in your tank may have taken a ride on the fish you just bought at the store. However, in many cases, the single celled organisms were carried through the air until it landed in the tank and started to grow. All it needs is enough light and micronutrients to grow.


Aquarium Algae

Is algae bad or good for fish in tank?

There is no way that the average fish tank can contain enough algae to produce the oxygen fish need, so don’t let the algae create a layer of scum on the inside of the tank and call it a good thing.

A little alga is fine, and healthy tanks will have a little alga. It is something that many fish will graze on. It helps reduce the nitrate and phosphate in the tank. The problems arise when there is too much algae in the tank. Furthermore, you have a serious problem if the nitrates and phosphates are so bad that the algae is overgrown or comes back just as bad shortly after you clean the tank.

Note that not all algae are good. Good algae will be green and grow hair-like fronds if left alone. Any brown or red algae indicate a problem with the water quality. It could mean your new tank is not ecologically balanced, or it means there is too much nitrate and/or phosphate in the water. Black “algae” is actually cyanobacteria. They grow in water with too much phosphate, and they’re a particular bane of coral aquariums

If you have real algae growing in the tank, it will be a fine green layer that gets worse with time, eventually growing those fronds we mentioned. If your tank forms small green dots on the sides, that isn’t algae but diatoms. These need to be removed.

Is too much algae bad for fish?

Any red, black or brown algae are bad for fish and needs to be treated immediately. A little green algae is fine.

If there’s a heavy level of algae in the tank, it means there are problems like excess nitrates, insufficient oxygen, excess phosphates or other problems that can kill your fish. Sometimes the real reason for the algae and sick fish is over-crowding of the fish tank.

The only caveat to that is that algae so thick it starts dying off can kill your fish. As the algae dies in mass, it sucks oxygen out of the water. In this case, the fish can suffocate.

Is green algae good for aquarium?

A little aquarium algae is fine and really unavoidable. Too much is a problem, especially if it clogs a water purifier or affects the water quality.

Can algae kill fish in tank?

Toxic algae will kill fish if there is too much of it. In other cases, the algae don’t kill the fish. Instead, the toxic levels of nitrates, phosphates and carbon dioxide in the tank kill the fish. If the algae itself is rotting in the tank, your fish are dying because the water isn’t clean enough for them to live in. An algae die-off will pull oxygen from the tank and could suffocate the fish, too.

What makes algae grow in a fish tank?

Algae are a simple plant. It needs nutrients and light to grow. True algae will always be present in the tank at some level. Too much indicates a problem with water quality.

How do I reduce algae in my aquarium?

The algae growing in a film on the glass wall of the tank is actually the best type for the fish – in moderate. You can reduce it by cleaning it off. It will return in waves, so you’ll need to clean it off periodically. You can deal with this type of algae naturally by getting shrimp, hermit crabs and snails that will feed on it.

The algae growing on rockwork or the sand bed is generally healthy. You can put goby fish in the tank that eat this type of algae. Your next line of defense is physical, removing the rocks and scrubbing off the algae. You can add bacteria or phosphate limiting chemicals to the water to control this type of algae.

If you have bryopsis, a type of thick hair algae that grows on rocks and sand, you have a challenge on your hands. This alga survives when you turn down the lights and limit the nutrients available for it. Fluconazole treatment will kill this alga without harming your fish or your coral.

You can try to limit algae growth by dimming your lights for a few weeks. Covering a tank with a trash bag for a few days will starve the algae, but it will hurt the xoazanthellae in coral, too. You’ll need to increase the oxygen flow through the tank.

Algae feed on the nitrates from fish urine and phosphates in their waste. Cleaning the fish tank to remove this waste and changing out the water can reduce the algae levels. Increasing the amount of water filtration also reduces the amount of food the algae have.

Maintain your filter media! You may need to upgrade the filter media with something that can remove phosphate and carbon (it removes dissolved organics). The media will need to be changed at least once a month. If the filter is saturated, it may leach the bad stuff back into the tank – a feeding frenzy for algae.

A common mistake that feeds algae is over-feeding your fish. Only give your fish enough food to be consumed in a few minutes. Those extra little flakes drifting to the bottom of the tank rot, creating fertilizer for algae growth. You can try to soak up excess nitrates and phosphates by adding packets of neutralizer to the tank. Siphon up the sludge at the bottom of the tank in case you have dead plant matter and rotting food lodged in the gravel layer.

If you have red slime algae, the red cyanobacterium we warned against, you need to eradicate it as quickly as possible. You need to improve the water quality and increase the oxygen levels