One-eighth of a teaspoon should be sufficient.. It does say, however, on the bag that 1/2 to 1 pack of the soluble will treat a gallon of water so I'm not exactly sure. One teaspoon is equal to 5687 milligrams and that's over seven times the maximum recommended dose. Dividing that by eight, you get 710 milligrams which is the closest you can get without exceeding the maximum dose. I'd suggest you ask the company if this isn't much help, although I hope it is!! Best of luck with you flock!!