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Metronidazole - Fish Medication Information


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Metronidazole (Flagyl)


What It Treats – Internal parasites (flagellates), Brooklynella, Uronema marinum.


How To Treat – Metro can be found as a stand-alone drug (e.g. Seachem MetroPlex, Hikari Metro+) or incorporated into a multi-purpose medication (e.g. API General Cure). When using 100% metronidazole powder, I dose 500 mg for every 20-40 gallons (80-160 liters). I typically start on the low end (500 mg per 40 gals), and then ramp it up to 500 mg per 20 gals by the 3rd or 4th dose. For brook & uronema, dose directly into a quarantine tank every 48 hours for 10-14 days. For intestinal worms, it is best to soak metro in the fish’s food. Use Seachem Focus to bind it to the food, and feed daily for up to 3 weeks or until symptoms (white stringy poop) disappear. My recipe for food soaking metro (and prazi) can be found below:


Using a shot glass:
1 scoop (~ 1/8 teaspoon) of medication
1 scoop Seachem Focus (this makes it reef safe)
1 tbsp food (preferably pellets or frozen food)
A pinch of Epsom salt to help expel dead worms/parasites
A few drops of saltwater or fish vitamins
Stir until a medicated food slurry has been achieved
Feed after soaking for 30 mins
Refrigerate or freeze any leftovers for future use


Whether or not metro is “reef safe” is a topic for debate. The general consensus is that while soaking it in fish food IS “reef safe,” dosing it directly into the water column IS NOT and should only be done in quarantine.


Pros – Can be soaked in fish food, making it reef safe. However, Seachem Focus needs to be used to prevent the medication from leaching out. Also, it is a good idea to run carbon just in a case. ;)


Cons/Side Effects – Certain fish seem to have a negative reaction/side effects to metronidazole; however this is rare.

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