Coral pests can wipe out frags fast. Many start small and hide well. Good identification saves time and coral tissue.
This guide helps you spot common pests early. You will learn what to look for and what to do next. Use it during inspections and quarantine.
Start with a smart inspection routine
Do inspections under white light and blue light. Use a small flashlight and a magnifier. Check new frags before they touch your display.
Pull the coral plug and inspect the underside. Many pests lay eggs on the plug rim. Look for clusters that resemble sesame seeds or jelly dots.
Use a turkey baster to blast the coral. Watch what flies off into a white container. Many pests detach when disturbed.
Track coral behavior over a week. Polyps that stay closed can signal irritation. Tissue loss at the base can signal a hidden grazer.
- Inspect for 3–5 minutes per frag before placement.
- Use a white bowl to spot tiny moving dots.
- Photograph the frag weekly to catch slow changes.
For a full quarantine workflow, see reef tank quarantine basics. It pairs well with pest checks. It also reduces disease risk.
Common coral pests and what they look like
Acropora-eating flatworms often cause pale bite marks. You may see missing tissue on branch tips. Adults look like tan ovals, about 2–4 mm long.
Montipora-eating nudibranchs target caps and encrusters. They match the coral color and hide in folds. Eggs look like white spirals, often on shaded edges.
Red bugs are tiny yellow specks on Acropora. They cluster on smooth skin and around polyps. Polyps retract and growth slows over 1–3 weeks.
Zoanthid-eating nudibranchs and spiders hit zoa gardens. Nudibranchs mimic zoa skirts and stalks. Spiders look like pale crabs with long legs.
- Flatworm signs: patchy paling and “bite” arcs on Acropora.
- Nudibranch signs: tissue loss plus visible egg spirals.
- Red bug signs: poor polyp extension and dull coloration.
Do not confuse pests with parameter stress. Rapid alkalinity swings can mimic bites. Keep alkalinity stable within 0.3 dKH per day.
Need a baseline? Review reef tank water parameters for target ranges. Stable numbers make pest clues clearer. They also speed recovery after treatment.
Confirm, treat, and prevent re-infestation
Confirm pests by repeating a blast test after a dip. Use tank water in a small container. Match temperature within 1°F to reduce coral stress.
Use a coral dip for 5–15 minutes, per label. Agitate the coral every 2 minutes. Then rinse in clean tank water before returning to quarantine.
Eggs often survive dips. Plan a repeat schedule. For many pests, dip every 4–7 days for 3–4 rounds.
Remove and discard infected plugs when possible. Re-mount on new plugs or rubble. This cuts egg surfaces and speeds control.
- Quarantine new corals for 21–30 days in a separate tank.
- Keep salinity at 1.025–1.026 and temp at 77–79°F.
- Use a dedicated frag rack and tools for quarantine only.
Common mistake: treating once and stopping. Another mistake is dipping in cold water. A third mistake is skipping the underside inspection.
If tissue loss continues, check flow and alkalinity next. Increase random flow around SPS. Aim for nitrate 5–15 ppm and phosphate 0.03–0.10 ppm.
For more on dips and timing, read coral dip guide. It covers mixing, rinsing, and repeat plans. It also lists safe observation cues.
Coral pest identification is a skill you build over time. Inspect every frag with the same routine. Combine quarantine, repeat dips, and stable parameters for best results.
When in doubt, document changes and act early. A fast response often saves the colony. Your display tank will stay cleaner and more predictable.
Sources: Borneman, E. (2001) Aquarium Corals; Sprung, J. (2005) Corals: A Quick Reference Guide; Delbeek & Sprung (1994–2005) The Reef Aquarium Vol. 1–3
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