Coral care guide
Zoanthid Coral Care Guide
Zoanthids—usually shortened to “zoas”—can turn a small patch of rock into a field of color. They are adaptable, fast-growing under the right conditions and available in enough named morphs to make sensible people start discussing individual polyps.
Hardy does not mean indestructible. Stable water, reasonable light and clean polyps matter more than the name on the plug.
What is a Zoanthid?
“Zoanthid” is a broad hobby term for colonial polyps in the order Zoantharia. Most aquarium zoas are sold as Zoanthus or Palythoa, but trade names are color labels rather than scientific identifications. Unless a coral has been examined properly, treat a confident species name on a retail tag with caution.
Colonies spread across rock through connected tissue. That growth habit makes zoas excellent for islands and garden-style displays, but it also means a healthy colony can reach neighboring rockwork faster than expected.
Quick care guide
| Requirement | Recommended starting point |
|---|---|
| Care level | Easy to moderate |
| Lighting | Low to moderate; roughly 50–150 PAR depending on the morph |
| Flow | Moderate, indirect and varied |
| Placement | Lower to middle reef; isolated rock when spread must be controlled |
| Feeding | Optional; fine suspended foods or very small meaty foods |
| Temperament | Can overgrow or irritate neighboring corals |
| Temperature | 76–79°F |
| Salinity | 1.025–1.026 specific gravity |
| Alkalinity | Approximately 7–9 dKH, kept stable |
| Nutrients | Detectable nitrate and phosphate without abrupt swings |
These are starting points. Zoanthid morphs respond differently, and a colony already adapted to one system may need time to adjust to another.
Lighting
Most zoas do well under low-to-moderate light. Around 50–150 PAR covers a useful starting range, with unfamiliar or recently shipped frags beginning near the lower end. Increase intensity gradually after the polyps are opening reliably.
Too much light too quickly can cause persistent closure, paling or a washed-out appearance. Too little light may produce stretching, slower growth or darker coloration. Spectrum also changes how a morph looks: fluorescent skirts and oral discs will appear very different under heavy actinic lighting than under a balanced daytime spectrum.
Do not chase color by moving the frag every day. Give it time to respond to one stable location.
Water flow
Use enough varied flow to keep debris and mucus from settling between polyps without folding the colony over or keeping it shut. The skirts should move gently rather than being pinned in one direction.
Persistent debris between polyps favors algae and irritation. A narrow pump stream, however, can keep an otherwise healthy colony closed. Adjust the direction before assuming the coral needs more flow everywhere.
Placement and controlling growth
Start new zoas in the lower-to-middle reef on a stable surface. An isolated rock or removable tile is useful for fast-growing morphs because it keeps the colony from crossing directly onto the main structure.
Leave space around slower corals. Zoas do not need dramatic sweeper tentacles to become difficult neighbors; they can simply grow over available surfaces and shade or irritate what is already there.
Feeding
Zoanthids receive much of their energy from their photosynthetic symbionts and do not require heavy direct feeding. Fine suspended foods, small frozen particles and nutrients already present in a well-fed reef may support growth.
If you feed directly, use very small portions and restore normal circulation after the colony has had time to respond. Food that sits between closed polyps is pollution, not a growth strategy.
Water chemistry and nutrients
Zoas generally tolerate a wider chemistry range than many stony corals, but they still respond poorly to rapid change. Keep temperature and salinity stable, avoid abrupt alkalinity corrections and maintain measurable nitrate and phosphate.
An aquarium stripped to undetectable nutrients can produce pale, stalled colonies. Chronic excess can encourage algae and detritus around the mat. The useful target is a stable, biologically active reef—not a competition to make both nutrient tests read zero.
Zoanthid pests and irritation
Closed polyps are a symptom, not a diagnosis. Inspect the colony and plug under white light for:
- Zoanthid-eating nudibranchs and their egg spirals
- Sundial snails or other unfamiliar snails on the colony
- Spiders or small crustaceans moving between polyps
- Algae, cyanobacteria, vermetid mucus or sediment covering the mat
- Fish or invertebrates repeatedly picking at the colony
- Fresh tissue damage, melting or an unpleasant odor
Quarantine new coral when possible. Use only a coral dip appropriate for the animal, follow the current product label and remember that many dips affect mobile pests without reliably killing eggs. Inspection and follow-up matter.
Palytoxin and safe handling
Some zoanthids can contain palytoxin, and appearance cannot reliably tell you which colonies present a hazard. The CDC has documented serious aquarium-related exposures through inhalation, eye contact and damaged skin. Read the CDC investigation and safety discussion.
- Wear gloves and eye protection when handling, cutting or cleaning zoanthids.
- Cover cuts and keep hands away from your face.
- Never boil, bake, steam or use hot water on zoanthids or rock that may contain them.
- Avoid procedures that create spray or aerosols.
- Keep children and pets away from the work area and dispose of water safely.
- Clean tools and surfaces after use without mixing household chemicals.
If exposure is followed by breathing difficulty, chest pain, severe eye irritation, fever or systemic illness, leave the area and seek urgent medical help. In the United States, Poison Control is available at 1-800-222-1222. Call emergency services for severe symptoms.
Acclimating new zoas
- Confirm the coral and shipping water are not experiencing a dangerous temperature difference.
- Inspect the polyps, mat, plug and underside under white light.
- Follow a trusted quarantine and coral-dip process without mixing treatments.
- Discard shipping and dip water rather than adding it to the aquarium.
- Begin in modest light with moderate indirect flow.
- Allow several days of stable conditions before moving the frag repeatedly.
Some polyps may remain closed after shipping. Steady improvement is more informative than whether every polyp opens on the first afternoon.
Troubleshooting
| Symptom | Check first | Practical response |
|---|---|---|
| Whole colony closed | Recent changes, temperature, salinity, flow and light | Correct confirmed instability and stop making simultaneous changes |
| A few polyps closed | Local debris, pest, sting or fish contact | Inspect under white light and remove the specific irritant |
| Long stalks or stretching | Insufficient light or shading | Increase exposure gradually after ruling out other stress |
| Pale or washed out | Rapid light increase, temperature or very low nutrients | Reduce abrupt stress and acclimate gradually |
| Algae around the mat | Detritus, flow and available nutrients | Improve varied flow and clean carefully without damaging tissue |
| Colony shrinking or melting | Pest, infection, severe instability or tissue damage | Isolate when practical and act promptly on the confirmed cause |
For a more detailed diagnostic sequence, read Why Are My Zoanthids Not Opening?.
Final take
Give zoas stable water, modest light, clean indirect flow and enough room to spread. Inspect new arrivals carefully and handle every colony as though palytoxin may be present. The fanciest trade name in the tank still benefits from ordinary good husbandry.