Doxycycline exert a bactericidal action on gram positive and gram negative bacteria. Useful for control of some common bacterial diseases of fish including septicemia, mouth rot, and fin and tail rot. Each single packet contains: doxycycline hyclate(active)..............................100 mgDirections: Tablets Only Add 1 tablet (100 mg) into aquarium for every 15 gallons of water to be treated. Repeat in 24 hours. It is suggested that a partial water change be made between treatments. While duration of treatment depends on type and severity of infection, it is recommended that extended medication baths continue for a minimum of 5 days but not more than 10 days. Discontinue treatment if no improvement is noted within 5 days. To remove harmless yellow color, change 20% of water and use charcoal filter until clear.Caution: Fish Antibiotics are for aquarium and ornamental fish only. Not for human use. Keep out of the reach of children. Keep container tightly closed and in a cool dry place. Not to be given to fish intended for human consumption. Storage: Keep lid tightly fastened and store at controlled room temperature of 59°-86°F. (15°-30°C).