Yellow Algae in a Saltwater Tank: How to Get Rid of It? Is It Harmful?

Yellow algae is simply green algae lacking nutrients. It is not harmful to your tank but will grow very quickly and needs to be maintained.

What is yellow algae?

Yellow algae is actually a form of green algae. It is green algae that has become resistant to sanitizers in the water, such as chlorine. Whereas green algae will typically float on the top of the water, yellow algae will attach itself to surfaces. This can be anything from the sides of your tank to the base of your tank and even other objects in the tank such as rocks.

So, there is no set reason why green algae will turn into yellow algae. In fact, it may be a good indication that something is wrong with your tank.

This could be anything from the levels of sanitizer to a lack of filtration. These incorrect levels can also affect the other plants and creatures living in your saltwater tank and so it is best to sort it out sooner rather than later.

Is yellow algae harmful to fish?

Although many people will be quick to want to get rid of any algae growing in their home aquarium it is not necessarily a bad thing. Any algae in your tank will happily absorb nitrates, phosphates, and other nutrients floating about in your tank, for example from fish waste. This can actually help to keep your tank’s ecosystem happy and healthy.

However, the main problem that many hobbyists have with yellow algae is the look. It can quickly become an eyesore and ruin the aesthetics of your home tank. It will encroach on all corners of your aquarium as it will attach itself to anything that it can find. 

However, despite these problems as long as it is kept under control it is not harmful to fish. The main risk that it poses to the creatures in your home tank is it taking over and taking up all of the space. If you leave the yellow algae unattended for too long is may end up suffocating your fish as they get trapped in it.

What does yellow algae mean in a fish tank?

Yellow algae in a fish tank is an indication that something is not correct with your levels. However, it is not any more specific than this. You will need to check all of the levels in your tank yourself in order to determine what the problem is and what exactly is causing the yellow algae.

A few main things to check are: 

  • The pH level of your water
  • That the filtration system is working correctly
  • The sanitizer levels
  • The lighting

The chances are that one of these levels is out of balance and will be the cause of yellow algae as opposed to green algae. Once you have correctly identified the root cause of the problem make sure that you get it sorted as soon as possible in order not to pose any risk to your tank.

Is algae bad for saltwater tanks?

Despite popular belief, algae is actually a useful addition to your saltwater tank. Not only does it provide a source of nutrients and food to your fish, you may see them nibble on it in between meals, but it will also help to keep your tank clean. 

The waste from your fish will be partially absorbed by the algae. Nutrients such as phosphates and nitrates are absorbed by algae. In fact, saltwater algae is commonly used as a type of filtration method for tanks, although typically this is done with microalgae.

It is not all good news though. If you decide to keep algae in your saltwater tank then you must be prepared to tend to it. It will grow quickly and spread throughout your tank like wildfire. However, there are a few things that you can do to actually limit the growth of your algae.

These include:

  • Limiting the amount of light that your tank gets (think 10-12 hours each day max)
  • Limit the amount of nutrients in your tank (that are available to algae)
  • Have water changes regularly (bad water conditions often help algae grow)
  • Do not overfeed your fish (the algae will absorb the extra nutrients)

If you manage to keep your algae under control then you will easily reap the benefits of having it in your saltwater tank!

How do I get rid of algae in my saltwater tank?

There is no set method for removing algae from a saltwater tank. The process that works best for you is dependent on how much effort you are willing to put in and also how much algae you want to remove. If you find that you are having to remove a lot of algae very often then perhaps it is worth considering removing it altogether.

Removing algae by hand

The first way that you can remove algae from your home tank is to remove it by hand. This can involve a lot of effort as you will need to first put on a protective pair of gloves (if you have any creatures that may bite you, any chemicals in the water etc.) and then pull the algae from your tank using your hands. 

Using this method will allow you the most control over how much algae you remove from your tank as well as exactly where you remove it from. This will allow you to free rocks, corals and other items from the algae but leave the algae in a desirable place in your home aquarium.

Clean up crew

If you prefer a more passive approach then consider adding snails and certain fish to your tank. These creatures will happily munch away on the algae. However, just like anything they can bring their own problems. For example, snails can multiply very quickly.


Having yellow algae in your tank is not a bad thing, it just means that you need to adjust your levels. Once you have done this you should see the algae return to its naturally green state.

If you find that the algae is becoming a problem there are ways to deal with it such as removing it by hand or adding creatures that eat algae to your tank.