This guide is written as an operating framework. Exact limits still depend on the organism, system volume, equipment and local rules.
Confirm the organism
Hydra are fixed polyps with tentacles. Planaria glide and often have a triangular head. Rhabdocoela and detritus worms are different.
Reduce excess food
Protein-rich leftovers can support planaria and hydra prey. Improve feeding accuracy and remove waste.
Protect the most vulnerable livestock
Move valuable eggs, tiny fry or shrimplets to a clean prepared system when immediate predation risk is high.
Trap and remove
Siphoning, traps and repeated inspection can reduce numbers without exposing every animal to medication.
Check treatment compatibility
Many flatworm treatments can harm snails or cause secondary water-quality problems when organisms die. Plan water changes and carbon use before dosing.
Research and review
This is original AquaNexus writing. It does not reproduce third-party articles, tables, photographs or databases. Species-specific legal and husbandry claims must be checked against current authoritative sources before publication as final guidance.