Metronidazole: Treats internal parasites (flagellates), Brooklynella, Uronema marinum. How To Treat - Metro can be found as a stand-alone drug (ex. Seachem MetroPlex, FishVet Metro-MS, Hikari Metro+) or incorporated into a multi-purpose medication (ex. API General Cure). 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 until symptoms (white stringy poop) are gone. For brook & uronema, dose the medication directly into a quarantine tank for at least 10 days. 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. When using straight 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 slowly ramp it up to 2x that if I'm not seeing positive results from the lower dosage. Too much metro too soon will kill certain fish.