If I understand this correclty, the directions say to dissolve the powder in a Gallon of water, to arrive at a concentration of 400mg/gallon. This should be all that is required for reconstitution.
The question is WHAT IS THE DOSE (not concentration) that you're supposed to be giving the bird??? For example, if the bird needs 100mg, he needs to drink 1/4 gallon of medicine. That seems like a TON.
How many birds are you supposed to be able to treat with a gallon of medicine? Or is it just a matter of leaving that gallon out for a specified number of days--knowing that the animal scientists who formulted the medicine know how much to expect the bird to drink over several days. (Most human antibiotics are given 10-14 days.)