Zoanthid Pests: How To Remove These Unwanted Visitors

Have you noticed a naughty hitchhiker? Who are you going to call…well, not the ghostbusters this time! With this Zoanthid pest guide, you are not only going to hopefully remove these unwanted residents, but you should also know how to identify them next time they make an appearance. 

Zoanthids, also known as Zoas, are hardy corals that come in a wide range of colors and crazy names! Corals are unfortunately not immune to diseases and pests. Occasionally, pests are introduced when you place new additions in your aquarium, which is why pre-treatments and quarantining new inhabitants are extremely important. 

Common pests and diseases you may encounter on your Zoanthid-keeping journey may include: 

  • Zoanthid Eating Nudibranchs
  • Sea Spiders
  • Sundial Snails
  • Zoa Pox

The more experienced you become, the more “normal” it gets to carry out routine checks to manage pests that make the odd appearance! As years pass, more and more new techniques and products are evolving to help mitigate hitchhikers, however, some pests can resist these treatments and can quickly cause utter chaos inside your aquarium!

Caution When Removing Pests!

Before you tackle your pest or disease issue, there are a few things you must consider, to protect yourself.

If you didn’t already know, some Zoanthids contain a nasty toxin called palytoxin. Palytoxin is so dangerous as it binds to the sodium-potassium pump found inside our cell membranes. Sodium-potassium is essential for biological processes, such as ion movement inside our cells. 

As the toxin is embedded inside the coral’s flesh, it is only an issue if the colony becomes damaged. Therefore, always take extra care when handling polyps, especially if you have any open wounds when treating your Zoanthid. Protective gear such as gloves and goggles are recommended. If you think the toxin has entered your skin, seek emergency medical treatment immediately.

How To Get Rid Of Zoanthid Eating Nudibranchs?

If you have ever seen a photo of a nudibranch, I’m sure you would agree with how cute and colorful they look! Your Zoa, however, may think otherwise when the “cute-looking” nudibranch starts munching on their polyps. 

Zoa Eating Nudibranchs are pests and should be removed from your aquarium immediately. A nudibranch (nudi), commonly known as a sea slug, is an aeolid gastropod mollusk that is a fairly clever Zoanthid pest. As they consume your Zoa, they take on your Zoas color and fluorescence, making them very difficult to find – they are hide-and-seek champions!

Another issue is the nudibranch’s sexual behavior… As they are hermaphrodites both parents can become pregnant, so, if you have spotted at least two nudis crawling around, it’s likely they have successfully reproduced. This impressive strategy to increase their population is not good news for your Zoanthid. 

Chemical Removal Techniques:

Many hobbyists use commercially available dips such as CoralRX to treat corals in the quarantine period – we also recommend this approach to try and eliminate them before your coral even touches the aquarium water. If you do opt for CoralRX, ensure you thoroughly research the dipping times for your type of Zoanthid (as this can differ between species) and always follow the manufacturer’s instructions and guidance. 

As they like to hide in your Zoanthid’s mat, you should start there. Grab a pipette with your CoralRX solution and wash between your Zoanthid’s polyps and around the bottom base of your Zoa frag. 

After you have removed the nudibranchs, the next step would be to eradicate their eggs. As they hatch within 10-14 days, you need to act fairly fast! Nudibranchs lay their eggs in a ribbon-like spiral that have a thick gel making them difficult for you to remove, however removing them by hand using a dry paper towel seems to be successful in pulling them off your Zoanthid’s polyp. 

Once you have removed the eggs, come back and check frequently for more eggs in case you missed a nudi hiding somewhere in your aquarium.

Physical Removal Techniques:

You can also try removing Zoa Eating Nudis with tweezers – just be sure to sterilize them before you do your eyebrows! 

How To Get Rid Of Sea Spiders?

Sea Spiders are not like the spiders you find around the house. Even though they are members of the arachnid family, they are in fact marine arthropods, known as Pycnogonida. 

Depending on which of the 1300+ known species of Sea Spider you have in your aquarium, will determine if it will feast on your Zoanthid, however almost all of them are carnivores, so the likeliness of these common predators causing damage is highly likely. 

As some Sea Spiders have a diameter of 0.04 inches, their small size can make it very difficult to spot in an aquarium, especially when they do their disappearing act and hide inside a closed polyp. 

Chemical Removal Techniques:

Some commercial treatments claim to remove Sea Spiders, however many experienced hobbyists will disagree with this because Sea Spiders tend to lay between the mucus layer of corals. The mucus it sits in creates a protective layer for the spiders. 

Therefore, the best technique would be physical removal. 

Physical Removal Techniques:

Your best bet is to remove them with a pair of tweezers or suck them out with a turkey baster and keep checking for possible hatched eggs. Unless you cut open your Zoanthid, you are unlikely to see any Sea Spider eggs. Sea Spiders are very clever parents. Instead of laying eggs freely in the water, they will climb onto your Zoanthid’s mouth and lay their eggs inside the polyp. When the eggs hatch, your Zoa’s polyp will start to disintegrate.

There has been no success in Sea Spider egg removal yet because they reside so deep within your Zoa’s tissues, so you will have to wait until they hatch to remove them. 

How To Get Rid Of Sundial Snails?

While snails may seem harmless, Sundial/Box Snails (Heliacus variegatus) are small predatory snails that will enjoy feasting on your Zoanthid. You want to be looking out for a snail with a flat black and white spiral (scientifically called a discoidal) shell with a little protrusion on the back.

If they have already munched their way through your Zoanthids they will soon move onto other corals in your aquarium, therefore, you will want to remove them asap!

Luckily, they are fairly easy to see, so take a quick look at your Zoanthid before adding it into your aquarium. Remove any that have possibly hitchhiked this far and check your Zoanthid periodically because Sundial Snails spend a long time in a free-swimming larval stage. 

To prevent Sundial Snails getting into your aquarium in the first place, it is recommended to quarantine your Zoanthid for 3 months, monitoring your Zoa on a daily basis for any snails to make an appearance, this is usually when the lights are turned off – sneaky snails!

Chemical Removal Techniques:

If you haven’t got the time to physically remove them, or they are well hidden, CoralRX is going to be your best friend!

When your Zoanthid is in CoralRX, you should also grab a turkey baster and blast your Zoanthid, so you can get between your Zoa’s polyps.

Physical Removal Techniques:

Manual removal is probably a better method for getting rid of them. When Sundial Snails are feeding, your Zoanthid colony will close up, which makes it relatively easy to locate them, especially if you have a large Zoa garden.

How To Get Rid Of Zoa Pox?

Zoa Pox (also known as Zoopox) is a disease that causes tissue recession and eventually death if not treated.

Similar to the contagious chickenpox we are very familiar with, your Zoanthid will soon be covered in pimples. The pimples will be a yellowish-white color and will cover your Zoa’s stalk and mat. Once infected, your Zoanthid will close its polyps and die. As it is contagious, it can spread to other Zoa colonies in your aquarium, therefore rapid treatment is needed. 

Even though the causes of Zoa Pox are not completely known, early detection and treatment can improve the chances of your Zoanthid surviving an outbreak. 

Chemical Removal Techniques:

Using a freshwater fish medicine, called Furan-2, is the only known treatment of Zoa Pox. This can either be done during your Zoanthids quarantine period or as a quick dip once you notice an infected Zoa. Unfortunately, now it seems Furan-2 has been discontinued. Give your local fish store (LFS) a call and check they haven’t got a box out the back, as some hobbyists have been successful. If not, do not worry. You can try a Nitrofurazone-based aquatic treatment, as nitrofurazone is an active ingredient in Furan-2. However, if you use nitrofurazone, check with your LFS for dosage directions, as these may differ for corals as it is also a product marketed for fish. Another treatment you could try would be CoralRX. CoralRX is used to treat corals that have known parasites or other bacterial infections. It is also the most common treatment used before adding live corals into reef aquariums. 

Treating Corals With Furan-2

API’s Furan-2 has been effective for fighting Zoa Pox for many hobbyists, which is why it is the only known “go-to” treatment for infected Zoanthids. 


  1. Place freshly mixed saltwater into a container. You should avoid using aquarium water to ensure that the water isn’t infected by the Zoa Pox outbreak. Check that the temperature, salinity, and pH of the newly mixed saltwater matches your aquarium water parameters – you do not want to stress your Zoanthid more. 
  2. Take one cup of the salt water and mix it with one packet of Furan-2. 
  3. Place your Zoa in a container with the Furan-2 and saltwater mix. If your Zoa colony is not fully submerged, mix up the same ratio.
  4. Leave your Zoa to soak in the mix for 15-20 minutes. 
  5. With the remaining saltwater-only solution, rinse your Zoa. 
  6. If possible, it is recommended to place your Zoa in a separate quarantine tank, if this is not possible, place your Zoa back into the main aquarium. 

Allow 24 hours before repeating the treatment again. It is recommended to repeat treatment for two more days. 

After the third (and final) treatment, you should let your Zoanthid rest for 7 days and monitor its condition before repeating any further treatment. 

Treating Corals With CoralRX

Depending on which CoralRX product you buy, will depend on the recommended treatment. After shaking your bottle of CoralRX, you will need to create the dip.

Dosage per gallon (3.8 liters) of aquarium water:

  • CoralRX: 20 ml or 4 caps of solution per gallon. 
  • CoralRX Pro: 30 drops of solution per gallon.
  • CoralRX Industrial: 10 drops of solution per gallon.


  1. Grab a container and pour the dip in. 
  2. Place your Zoanthid in the dip and gently shake it, or if you have a spare powerhead, use that to keep a constant water flow. 
  3. While your Zoa is in the dip, take a turkey baster and blast your Zoa with the dip solution, ensuring you reach between the polyps and the underside. 
  4. Continue to do this for 5-10 minutes.
  5. After 5-10 minutes, discard the coral dip and rinse your Zoanthid with clean aquarium water. Your Zoanthid should hopefully be pest-free!


Hitchhikers are something that every hobbyist will likely experience at least once in the reef-keeping world. Once identified, there are some great physical and chemical ways to prevent and remove pests in reef aquariums such as API’s Furan-2 and CoralRX. 

However, if your Zoa still doesn’t make it after trying everything possible, do not be too hard on yourself…some corals never achieve a 100% success rate.

We wish you the best of luck treating your Zoanthid, and happy reefing!

  • Roy Lee

    I have an unhealthy obsession with reef keeping and maintaining successful tanks. If you haven't noticed from the website, I love everything related to saltwater tanks like coral, fish, and everything else in between.

    http://reeftankadvisor.com reeftankroy@gmail.com Lee Roy

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