Soft Coral Pest Guide: Zoa Pox, Nudis, and More

The Pests That Target Soft Corals

Soft corals are hardy, but not invincible. Here's a guide to the main pests and diseases, how to spot them, and how to deal with them.

Zoa-Eating Nudibranchs — Threat Level: HIGH

Tiny, translucent nudibranchs specifically adapted to feed on zoanthids. They match the colour of whatever zoa they're eating — absolute stealth predators.

Signs: Polyps not opening in a specific area, tiny egg spirals on plug undersides, colony slowly shrinking despite good conditions.

Treatment:

Dip every new frag — Coral Rx, diluted Bayer, or Revive. This is the single most important prevention step
For infestations: remove, dip, manually remove visible nudis and eggs
Repeat dips every 3-4 days for two weeks to catch newly hatched nudis
Wrasses (six-line, melanurus) provide long-term biological control

Zoa Pox — Threat Level: MEDIUM-HIGH

Small white or yellowish bumps on zoanthid polyps. Affected polyps close up and can eventually die.

Treatment: Furan-2 dip (15-20 minutes, repeat every other day for a week), improved water quality, and isolation of affected colonies. Some reefers report success with diluted Lugol's iodine dips.

Sundial Snails — Threat Level: MEDIUM

Small (5-10mm) flat-shelled snails that feed on zoanthids, usually introduced on frags. Most active at night — check with a red torch. Coral dips and wrasses deal with them effectively.

Flatworms — Threat Level: LOW-MEDIUM

Rust-coloured flatworms that cover corals and block light. Flatworm Exit works well but follow instructions carefully — dying flatworms release toxins, so run carbon and do a water change immediately after treatment.

General Prevention Protocol

Dip every new coral. No exceptions
Inspect with a magnifying glass after dipping — check plug undersides
Quarantine tank for 2-4 weeks catches most issues
Natural predators — wrasses are excellent pest control in appropriately sized tanks
Regular observation — most pests are spotted visually with careful inspection

The best time to deal with pests is before they enter the tank. What pests has everyone dealt with, and what worked?