White Flatworms in a Reef Tank: How Do You Get Rid of Them?

It takes time, effort, and money to put together the perfect reef tank, and as an owner, you are probably eager to protect your plants, fish, and coral to the best of your abilities. Perhaps you have invested in all the right things and taken all the necessary precautions, but then one day you spot them – flatworms. Now what?

Flatworms, or Planaria as they are also known as can cause damage to your tank and especially to your corals, but that can be avoided by taking action as soon as you realize they’re there. 

This article contains useful information and tips on how to get rid of flatworms in your reef tank, not only temporarily, but permanently. 

About Flatworms

Planaria, which is another word for flatworm, are organisms that every reef tank owner should be aware of. They can infest your tank when you least expect it and tend to be surprisingly hard to get rid of! You may think they are gone, only to have them come back within a week or two.

Flatworms are common in the United States, and chances are high you will come in contact with them sooner or later, and who knows, they might already live in your tank. The good news is that there are ways to get rid of them! 

First, let’s have a look at two different types of planaria (flatworm), to better understand what they are and the potential damage they cause.

Acropora-eating Flatworms

These white flatworms are also known as Acropora-eating flatworms, and they can cause substantial damage to your saltwater corals. These small, white, and oval-shaped worms appear to have a preference for different Acropora species, and they feed off coral tissue.

Once you notice that there are white flatworms in your tank – it is time to take action, as these work at an alarmingly fast rate. The white flatworm can be found in any saltwater tank, but they are often associated with Tricolor species and Staghorn coral, and if you have these in your tank you might want to be a little extra vigilant.

The species is currently unidentified and can, unfortunately, be difficult to spot due to the color. However, with a little bit of practice and by staying vigilant – even an inexperienced tank owner can learn to look out for these sneaky little worms. Flatworms like these are different from what are considered “regular” white flatworms.

Rust Brown Flatworms

The other type of flatworm is the Convolutriloba retrogemma – the rust-brown flatworm. These worms are, as indicated by their name, reddish, brown or rust-colored, and slightly longer and elongated than the white flatworm. 

Organisms like these reproduce fast and can spread before you even realize that they are there. There may be so many of them that they prevent your corals from getting the natural light they need to thrive, by simply sitting on the coral and blocking its access. 

While easier to spot and known to be less aggressive than white flatworms, these organisms are considered the most common flatworms – making them something to look out for in your reef tank. You don’t want worms to destroy what you have worked so hard to build because while they may be small with their 1/4″ in length, they can do a lot of damage.

Are Flatworms Bad for a Reef Tank?

The quick answer is that yes, it can be, but it isn’t the flatworm itself and more what the flatworm causes in the tank. When there are too many flatworms (which can happen quickly), they may block out sunlight, something that could have a harmful effect on the corral in your aquarium.

The rust-brown planaria do not eat coral, but there are indicators that the white flatworm does – undoubtedly harming the ecosystem you have created. Another problem is that the Planaria can harm fish if eaten, as they have potentially harmful toxins in their skin.

Getting Rid of Flatworms in the Tank

So, now that you have rust-brown or white flatworms in the reef tank, how do you get rid of them? The best strategy depends on what type of flatworm infestation you are dealing with, and the least desired types are the rust-brown flatworm and the Acropora-eating Flatworms, as these tend to cause the most damage. 


Unsurprisingly, preventing a flatworm infestation is the absolute best strategy. You can do this by using protein skimming and carbon as your weapons, and also by increasing the reef tank water flow. It is also recommended that whenever you bring in a new specimen – quarantine it first to avoid contamination.


There are a few species you can opt for keeping in your tank – known for eating flatworms. These probably won’t solve the problem in its entity if you already have a large infestation, as they may not be able to eat as many as it takes to eliminate the problem, but they can certainly be of help. Here are a few species known for consuming flatworm:

  • Blue Velvet Nudibranch (Chelidonura varians)
  • Leopard Wrasse (Macropharyngodon sp.)
  • Yellow Wrasse (H. chrysus),
  • Six Line Wrasse (P. hexataenia)

Some of these fish have very special requirements when it comes to the types of tanks they thrive in, so make sure your tank is suitable to house the fish of your choice.

Manual Removal

You may have to resort to removing the flatworms by yourself, manually, by using an appropriately sized syringe or airline tubing. This will require you to gently remove the flatworms one by one – without harming the coral – and while it can be somewhat time-consuming, it is worth the extra effort.


Some argue that the regular white flatworm eats the rust-brown flatworm and that it can therefore be beneficial, but when it comes down to it – you don’t want any type of flatworm in your reef tank. 

The best thing you can do is work to prevent them from inhabiting your tank, by increasing the water flow and using other preventive methods, or by adding species of fish known to eat flatworms. 

If the preventive methods fail and you end up with an infestation – don’t panic, and start considering your options. The key here is to make sure you protect your reef tank with gentle removal methods to cause as little additional disturbance as possible.


  • Living invertebrates – By Vicki Pearse, John Pearse, Midred Buchsbaum, Ralph Buchsbaum – 1987