Quick referencePolyclad/turbellarian flatworms (Convolutriloba retrogemma "rust brown" and Waminoa) coat reef rock + corals in flat brown patches. Smother coral; treat with Flatworm Exit + manual siphoning.
Symptoms
Brown flat worms 2-5mm on rocks
Brown patches on coral
Coral tissue recession
Worms visible on glass
Cause
Convolutriloba retrogemma + Waminoa flatworms hitchhike on coral + live rock. Reproduce rapidly - one worm becomes thousands in 2-4 weeks. Common entry point: SPS frags, zoanthid colonies.
Treatment options
Salifert Flatworm Exit. Standard treatment. CRITICAL: siphon ALL visible worms first. Dying flatworms release toxins; mass die-off can kill the tank.
Manual siphon. Powerful siphon hose into a 5-gallon bucket. Suck up worms before treatment. Repeat daily.
Six-line wrasse (predator). Pseudocheilinus hexataenia eats flatworms. Caveat: aggressive to other wrasses, may not survive QT.
Coral dip (Bayer). For new frags: dip in Bayer Advanced (imidacloprid) per manufacturer. Kills hitchhiker flatworms.
Always treat in a separate quarantine or hospital tank. Most medications are toxic to coral, invertebrates, and live rock biology. Consult an aquatic veterinarian for valuable fish.
Prevention
ALWAYS dip new corals in Bayer Advanced or CoralRx 5-15 minutes. Quarantine corals 4 weeks if possible. Siphon any visible flatworms immediately on sighting.
Fatality + outcome
Low directly. High indirectly - mass die-off after Flatworm Exit can crash a tank if siphoning is skipped.