For this product we require a completed Drug & Chemical Affidavit on file. If you have not submitted this form to us, please click here, and fax (813-671-8237) or email (fishsupplies@verizon.net) back to us. Thank You. Metronidazole is an effective and safe treatment for several protozoan and anaerobic bacterial diseases of fish (Cryptocaryon, Hexamita, Ichthyophthirius). It does not adversely affect the filter bed and is easily removed with carbon. There is little danger of overdosing. Usual dose is 125 mg/10 gallons. Info from Seachem