Can anyone tell me how to mix up the powder antibotics for my girls. I had one die on me and another one is beginning to sneeze or cough so I want to get a handle on this. The package says to mix a gallon at a time, but it says to use 400 to 800 mg and I'm old and didn't do well at math in school. I estimated about 1/8 of a teaspoon to a gallon, don't want to give them too much or too little. Can anyone help me?