pest · freshwater tank

Planaria (flatworms in freshwater)

Planaria are small flatworms (~1-5mm) that thrive in overfed shrimp/snail tanks. Not directly harmful to fish but compete for food and indicate excess nutrients.

Reviewed by Fast Aquatics husbandry team · Updated May 2026
Severity: Mild cosmetic - not directly harmful

Symptoms

What causes it

Overfeeding combined with established detritus. Planaria reproduce quickly when food + biofilm is abundant.

Treatment options

Always treat in a separate quarantine tank.

No Planaria (Genchem). Dose per manufacturer instructions. Safe for shrimp + snails. Most effective treatment.
Planaria trap. Glass trap with bait inside; collect and discard daily.
Reduce feeding. Cut feeding by 50% for 2 weeks. Population crashes when food source is removed.

Prevention

Don't overfeed shrimp tanks. Vacuum substrate during water changes.

Frequently asked questions

What does Planaria (flatworms in freshwater) look like?

Small white or tan flatworms on glass + decor. Worm population growing rapidly. Often visible at lights-out.

What causes Planaria (flatworms in freshwater)?

Overfeeding combined with established detritus. Planaria reproduce quickly when food + biofilm is abundant.

How is Planaria (flatworms in freshwater) treated?

No Planaria (Genchem): Dose per manufacturer instructions. Safe for shrimp + snails. Most effective treatment.

Can Planaria (flatworms in freshwater) be prevented?

Don't overfeed shrimp tanks. Vacuum substrate during water changes.

How fatal is Planaria (flatworms in freshwater)?

Mild cosmetic - not directly harmful

Related

Browse the full disease database for 45 aquarium conditions with treatment protocols, or check the care library for prevention-focused husbandry guides. Use our symptom matcher to rank likely diseases from observed signs, the water parameter checker to diagnose related water-quality issues, or the QT timeline calculator to plan a treatment schedule.