Zoanthid Care Guide

What are Zoas

Zoas are a small polyp, soft coral, meaning it does not have a skeleton. Most zoanthids grow outward from the original polyp, and essentially create a mat-like foot to grow from. Zoas are very colorful and far less picky about water parameters than most coral that do have skeletons.

Palys vs Zoas

Zoas are closely related to palythoa coral, with generally smaller polyps. Often, these names are used interchangeably describing both zoas and paly corals based on polyp size, though they are not the same. While pally polyps are typically the size of a dime or larger, there are some zoas that can reach that size as well. The lashes of the pally are generally (but not always) longer and a bit more scraggly.

Zoanthid Flow Requirements

Zoanthid flow requirement is typically moderate flow above the zoas. Too much flow can make it difficult for polyps to open up, but too little flow causes detritus and any other waste to settle around the coral. You can see if the zoanthid flow is too high if the zoas are leaning over, closed, or polyps are being blown over themselves. Too low of zoanthid flow can be seen with waste settling around the base of the polyps.

Like many other coral, zoas often react differently depending on flow. If there is more flow, zoas usually have short stalks, where lower flow may result in longer stalks. This can also be affected by lighting and genetic strain, so it should not be the only item considered in this case.

Zoanthid Lighting Requirements

Zoanthid are photosynthetic coral, however they do not demand nearly as much light as many other corals. Zoanthid Lighting Requirements for best growth and coloration will generally be blue and actinic spectrum lights, with around 50 to 150 PAR. Lower light may lead to reaching or longer stalks, as well as larger polyps. These are ways that zoas try to get more light. Too much light can cause zoas to shrink or algae to overgrow them.

For more about the different types of lighting, see the Reef Stable Saltwater Aquarium Lighting Guide.

Zoanthid Placement and Aggression

Zoanthids are not an aggressive coral, but placement can drive your success and growth rate. Beyond flow and lighting, zoanthids should be placed on flat surfaces. Zoas grow by spreading outward and struggle to grow on rocks that are too porous. By placing zoas on flat surfaces, you allow these zoanthids to grow more easily, and quickly. Another detail for zoanthid placement is that zoas will overgrow each other. For example, larger polyp zoas such as Salted Agaves will grow over and shade out smaller polyp zoas such as Pikachu Zoas. So for a nice zoa garden, keep similar size polyps together.

Zoanthid Feeding Requirements

Zoanthid Feeding is not required as they are a photosynthetic coral. That said, zoas will enjoy amino acid and vitamin supplements, as well as some occasional small foods like Reef Roids. While they may like occasional supplemental feeding, it is in no way required.

Zoanthid Temperature Requirements

The commonly agreed upon Zoanthid Temperature Requirements is the same as most corals, averaging at 78 degrees F. Zoanthids can survive in a wide range of temperatures, however 78 is the average. The best bet is to keep the temperature stable, within 1 degree F, for the best results!

Zoanthid Alkalinity, Calcium, and Magnesium Requirements

While maintaining stable Alkalinity, Calcium, and Magnesium is good practice overall, zoandthids do not have skeletons and therefore don't rapidly, if at all, consume these parameters. I would encourage general testing for overall reef tank health, but nothing specific is needed for zoas.

Zoanthid Nitrate and Phosphate Requirements

Though you don't want to be absolutely zero on Nitrates or Phosphates, you also don't want to be too high either. The ideal levels for Nitrate is between 1 and 10 ppm. Phosphate should be roughly 0.01-0.05ppm.

The reason for having some nitrate and phosphates in your tank is because research shows that coral need nutrients to enhance their growth and coloration. Too much of either, however, will slow growth and reduce coloration.

Myth: Zoas like Dirty Water

Many people believe that zoanthid grow best in "dirty" water. Which has turned into meaning zoanthids prefer high levels of nitrates and phosphates. There is not much evidence to support these zoanthid care claims.

This theory likely comes from how zoas grow in silty and more algae-inhabited water such as tide pools. Making their natural environment look "dirty".

Thoughts on Zoanthid Care from Tidal Gardens

Pests and Common Problems

Why are my Zoas Closed / Not Opening?

There are a number of reasons why zoas may not be open. If they are new to your reef tank, it may just be stress. In which case, it could take a few days for the zoas to open up.

Another reason zoanthids may not open is because of too much flow. If the flow is too heavy, the zoa may have a hard time opening and stays closed to protect itself.

Finally, there may be something picking on or eating the coral. Fish including angelfish (large and dwarf) as some inverts including emerald crabs may be nibbling on the coral. There are also a number common pests that may irritate the zoanthids.

Zoanthid Eating Nudibranch

Zoanthid Eating Nudibranch are small, slug-like creatures that take on the color of the corals they're eating. Learn more about Zoanthid Eating Nudibranchs.

Zoanthid Eating Spider (Sea Spider)

Zoanthid Eating Spiders (Sea Spiders) are small, spider-like creatures that are often found on or near corals or anemones they are eating. Learn more about Zoanthid Eating Spiders (Sea Spider).

Why are my Zoanthids are Melting?

Another problem with zoas is when they look like they are melting. Unfortunately, melting zoas typically means they are dying. This seems to be most common when there is a bacterial infection, the zoa has too much or too little light, or a pest is eating the zoa. Other parameter shifts or additives can also be a factor. For example, my zoas tend to melt whenever I dose vodka to the tank.

Why are my Zoanthids are inverted, like an umbrella?

When zoas open too far, they look like an umbrella. They will typically recover from this, however there are a couple of reasons that this may happen. The first is that there may not be enough light. If only one polyp is inverted, I would not adjust the lighting as is may just be a random occurrence.

Another, and one I have personally seen, is a feeding response. When they eat, rather than closing, some zoanthids open more. This is just a random occurrence and nothing to worry about.

Zoas are spitting brown slime?

Good news! If your zoas have a brown goo or slime coming from their mouths, it is typically nothing to worry about. Much like an anemone, this is usually just the coral's feces, or poop.

Palytoxin

I do have to make a note about palytoxin. Zoanthids and Palys can excrete one of the most deadly toxins known, palytoxin. The worst part, there is no known cure for it. Because of this, you should only handle zoas while wearing gloves, and keep them submerged at all times. This reduces the ability for the toxin to get in the air or your blood stream.

Though not overly common, some reefers have gotten very ill, or even died from this toxin. Many from cleaning pests off the coral / rock with hot water. Allowing this toxin to become airborne. Running activated carbon can help in the removal of the toxin from the water, but is not guaranteed.

As with many other corals and fish, it is VERY important to do research on proper zoanthid care and prevent potential illness.

Here is another reference on potential concerns with Palytoxin

Zoanthid Care Guide - Cheet Sheet

Temperature

• Zoanthids Prefer to be at roughly 78 degrees F.

Alkalinity

• Focus on stability, maintaining within 0.5 dKh
• Anywhere between 7-12 dKh

Calcium

• Focus on stability, within 25ppm.
• Zoas do not tend to rely on calcium as much. Any values in the safe range should be fine.

Magnesium

• Zoas do not tend to rely on magnesium as much. Any values in the safe range should be fine.

Nitrates and Phosphates

• The below numbers are ideal, but zoanthids can tolerate a wide range of nutrient levels.
• Nitrates: 1-10ppm
• Phosphates: 0.01 - 0.05ppm

Lighting

• Zoas are not overly picky on lighting. Provided the PAR is roughly 100, you should be fine.
• Blue and Actinic spectrum are best for color and growth.

Additional Coral Care Reading:

• Reef Stable - Acropora Care Guide
• Reef Stable - Montipora Care Guide
• Reef Stable - Euphillia Care Guide
• Reef Stable - Zoanthid Care Guide

Conclusion

Zoanthids are one of the easiest, most beautiful, and quickest growing coral! With this fast growth, zoanthids are also typically low cost as well. If you are looking for a good staring coral or just want to fill in the empty, lower light places in your reef tank, zoas are a perfect coral for you! With an infinite number of colors and patterns, you are almost guaranteed to find a zoa that matches you!

See what zoas Reef Stable has in stock!

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About the Author

John Krenzer

John is a Software Engineer with a passion for saltwater aquariums, as well as the founder and president of Reef Stable. He started in the aquarium hobby as a child with a 20 gallon freshwater aquarium. His interest in aquarium life grew and in 2008, John set up his first saltwater aquarium.

Today, John maintains a 120 gallon mixed reef aquarium as well as a 210 gallon aggressive species aquarium. These large tanks are contained within the same system, sharing a sump as a means to reduce total maintenance and increase total water volume.

John writes articles for the blog as a means to learn about more reef aquarium topics. These articles act as a reference for the readers as well as himself. John updates these articles frequently to provide additional information or make corrections as new information becomes available.

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