🐛 Flatworms (Planaria)

Flatworms are common reef aquarium pests that can quickly multiply to plague proportions. While some species are relatively harmless, others like Acropora-Eating Flatworms (AEFW) can devastate coral colonies. Identifying the type of flatworm you have is crucial for choosing the right treatment approach.

📋 Quick Facts

Type	Platyhelminthes (flatworms)
Appearance	Flat, oval, rust/brown/tan, 2-6mm
Severity	Moderate to High - depending on species
Common Entry	Hitchhiker on corals, live rock
Treatment Difficulty	Moderate - Effective treatments available

🔍 Types of Flatworms

1. Rust Brown Flatworms (Convolutriloba retrogemma)

The most common aquarium flatworm:

• Color: Rust, tan, or reddish-brown
• Size: 2-6mm, oval shaped
• Red dot: Often visible near one end
• Habitat: Glass, rocks, sand, low-flow areas
• Threat level: Moderate - block light from corals, release toxins when dying
• Reproduction: Extremely rapid in favorable conditions

2. Acropora-Eating Flatworms (AEFW)

Serious coral pest:

• Color: Matches host coral color (camouflaged)
• Size: 4-8mm
• Habitat: On and under Acropora corals
• Signs: Bite marks, tissue recession, egg clusters at coral base
• Threat level: High - can kill Acropora colonies
• Detection: Difficult due to camouflage; dip corals to confirm

3. Montipora-Eating Nudibranchs

Often confused with flatworms:

• Actually nudibranchs, not flatworms
• Oval, white/cream colored
• Leave distinctive egg spirals
• Treatment similar to AEFW

4. Zoanthid-Eating Flatworms

• Small, often matches zoanthid color
• Found on zoanthid polyps
• Causes polyps to stay closed
• Look for them at base of polyps

⚠️ Why They're Problematic

• Light blocking - Large numbers shade corals beneath them
• Coral eating - Some species consume coral tissue
• Toxin release - Dying flatworms release toxins that can kill fish
• Rapid reproduction - Populations can explode quickly
• Difficult detection - Coral-eating types are well camouflaged

💊 Treatment Options

For Rust Brown Flatworms

1. Flatworm Exit (Salifert)

The most common and effective treatment:

• Dose according to instructions
• Run carbon and do large water change immediately after
• Critical: Siphon out dead flatworms quickly
• Dying flatworms release toxins - have water change ready
• May need multiple treatments
• Safe for corals and fish when used correctly

2. Natural Predators

• Six Line Wrasse - Eats flatworms voraciously
• Yellow Wrasse - Good flatworm predator
• Leopard Wrasse - Hunts small invertebrates
• Mandarin Dragonet - May eat some flatworms
• Blue Velvet Nudibranch (Chelidonura varians) - Specialized flatworm predator

3. Manual Removal

• Siphon during water changes
• Turkey baster to blow them off surfaces
• Time-consuming but chemical-free
• Best combined with other methods

For Acropora-Eating Flatworms (AEFW)

1. Coral Dipping

Essential for all new Acropora:

• Use Bayer insecticide dip (most effective) or CoralRx
• Dip for 5-10 minutes
• Use airline tubing to blow into crevices
• Inspect coral carefully after dip
• Repeat dip in 5-7 days to catch hatching eggs

2. Bayer Dip Protocol

• Mix 10-15ml Bayer per liter of tank water
• Submerge coral, agitate gently
• Use turkey baster to blast base and undersides
• Watch for flatworms falling off
• Rinse in clean saltwater
• Dip again in 5-7 days

3. In-Tank Treatment

• Flatworm Exit may help but less effective on AEFW
• Wrasses provide ongoing predation
• Remove and dip affected colonies
• Quarantine all new Acropora

For Zoanthid Flatworms

• Freshwater dip (3-5 minutes in RODI water)
• CoralRx or similar coral dip
• Manual removal with tweezers
• Repeat treatments needed for eggs

⚠️ Important Warnings

Toxin Release

When flatworms die (especially rust brown), they release toxins:

• Can cause fish deaths if many die at once
• Always have large water change ready
• Run activated carbon during and after treatment
• Siphon out dead flatworms immediately
• Consider treating in sections if infestation is severe

⏱️ Treatment Protocol

Day	Action
1	Prepare water change, add carbon, treat with Flatworm Exit
1	Immediately siphon dead worms, 25-50% water change
3	Observe, manual removal of survivors
7	Second treatment if needed (eggs may have hatched)
14	Third treatment if any remain
21+	Add wrasse for ongoing control

🛡️ Prevention

• Quarantine all corals - Especially Acropora
• Dip all new corals - Before adding to display
• Inspect carefully - Look at base and undersides
• Keep flatworm-eating fish - Wrasses provide ongoing protection
• Dip twice - 5-7 days apart to catch hatching eggs
• Good flow - Flatworms prefer low-flow areas

❌ Common Mistakes

• Not preparing water change before treatment (toxin die-off kills fish)
• Single treatment only (eggs survive and hatch)
• Not dipping new corals (reintroducing pests)
• Ignoring small populations (they grow exponentially)
• Using Flatworm Exit on AEFW (less effective, need dipping)
• Not running carbon during treatment

📚 Summary

Flatworms are a common but manageable reef pest. Rust brown flatworms respond well to Flatworm Exit treatment combined with natural predators like wrasses. Coral-eating flatworms (AEFW) require more aggressive treatment with dipping protocols. Prevention through quarantine and dipping all new corals is the best long-term strategy. Always be prepared for the toxin release when treating - have water change ready and run carbon to protect your fish.