Yes, you mix it in one gallon of water, dosages in the chart are based on one gallon. If you want to make less than a gallon you can just reduce based on the amount of water. And recommendations are that it be made fresh each day. Coccidia are everywhere in the soil. When birds get infected with large numbers they get sick. The oocysts are shed in the droppings and are further spread that way. So keep feeders and waterers as clean as possible and free of droppings, don't let droppings build up where they live, to minimize spread. You can't get rid of them in the soil. Birds that are exposed and recover will have some resistance to whatever strain(s) they are exposed to. Wet, warm conditions can cause what is called a coccidia bloom, where numbers increase and can lead to outbreaks, so a warm, wet brooder is prime, which is why you hear so much about keeping brooder bedding dry. For chicks in a brooder, I start on day one giving them a dish of soil from my yard in a large plant saucer that they can dig and scratch and peck and dustbathe in. This exposes them to the microbes in the soil naturally and gives them a chance to build resistance while their immune systems are maturing, same way it would happen if they were outside with a broody hen. This has greatly reduced my incidence in my flock. I always keep Corid on hand in case I do see symptoms so I can treat quickly. The saucer is easy to dump and clean, and give fresh dirt/soil daily. If new birds are brought in then it's possible for them to bring in a new strain, or if birds are moved to new ground they can be exposed to a new strain, so those times it's good to keep an eye out for any symptoms. Some people use medicated chick feed, it contains a small amount of amprolium (the medication in Corid) which is supposed to help prevent outbreaks. I have never used medicated feed myself, I don't like to treat unless there is a reason. And even with medicated feed, if you do have an outbreak you will still need to treat with the full strength medication. I just keep the medication on hand and use when necessary. It's been 4 or 5 years since I've had an outbreak in my flock, or in any of my chicks, which I credit with the starting them on soil early in the brooder.