Metronidazole has been shown to be highly effective against internal and external flagellates. It is also effective against protozoan parasites such as Cryptocaryon in marine aquaria or against Hexamita and Ichthyophthirius.
Metronidazole is most commonly used to treat Cichlid disease due to the occurrence of Hexamita.
 
Treatment: Remove active carbon, Purigen, ChemiPure or other similar media that would remove medication from the tank. Turn off UV Sterilizers as well. Dosed at 1/4 teaspoon per 20 gallons of water after a 25% water change. Continue treatment for 7-10 days, max 14 days.
NOTE: There has been some confusion and controversy over the appropriate dosage. This is due to pure vs products with filler. In its pure form,
 
Other uses/treatment options:
Antibacterial Treatment: Metronidazole has proven to be effective against anaerobic bacteria, hence its recommendation as an antibiotic. However, we recommend using in combination with Neomycin, especially when attempting to treat bloat. Metro alone does not affect bacteria in an oxygenated environment due to overuse/abuse over the years which is why it isn’t commonly used as an antibacterial remedy.
 
Nematode or Trematode Treatment: Metronidazole is effective when used in combination with Praziquantel for internal parasites.
 
Fish Bath Treatment: Treat dechlorinated water or tank water in a small container at 1/8 teaspoon per 5 gallons. Leave fish in this bath for as long as tolerated. If concerned with cooling can add a heater.