The FDA, FARAD, and the mfg's say this:
Give amprolium at the 0.012% level as soon as coccidiosis is diagnosed and continue for three to five days. (In severe outbreaks, give amprolium at the 0.024% level.) Continue with 0.006% amprolium medicated water for an additional 1 to 2 weeks. No other source of drinking water should be available to the birds during this time. Make fresh daily.
So what does that mean?
0.024% = no less than 1.5 teaspoons per gallon
0.012% = no less than 3/4 teaspoons per gallon
0.006% = no less than 1/3 teaspoon per gallon
0.024% = no less than 2 teaspoons per gallon
0.012% = no less than 1 teaspoons per gallon
0.006% = no less than 1/2 teaspoon per gallon