FIX PEN 500 (Penicillin) treats various bacterial diseases in ornamental fish, such as pop-eyes, infected eyes, fin or tail rot, gill disease, columnaris disease, and skin ulcerations. Add one tablet (500 mg) to the aquarium for every 20 gallons of water. Repeat after 24 hours, and perform a partial water change between treatments. The duration of treatment should be based on the type and severity of the infection.  Typically, using the medication for a minimum of 5 days and a maximum of 10 days is recommended. If no improvement is observed within 5 days, discontinue treatment. Keep out of reach of children. The medication is strictly for aquarium use, intended only for ornamental fish and not for those intended for human consumption. Individuals allergic to penicillin should avoid contact with the treated water for three days post-treatment. Store with the lid tightly closed at a controlled temperature of 59°-86°F (15°-30°C).