Metronidazole is a highly pure, crystalline metronidazole. It is the most effective form available. It is effective against a vast array of parasitic infections ("hole in the head") with little danger of overdosage. It is easily removed through chemical filtration and is well tolerated by most invertebrates. Marine or freshwater. DIRECTIONS: Use 1 to 2 measures (each about 100 mg) for every 40 L (10 gallons). Repeat every 2 days as required. Turn off UV, ozone, and chemical filtration. To feed, blend 1 measure with about 1 tablespoon of frozen food paste. Food may be refrozen.