there really is no formula i can give you since how much coral you need depends in large part on your particular water chemistry, the tank size (the volume of water you're dealing with).
i'd start with perhaps a cup and place it in your filter in a cut off end of a nylon stocking or similar. it may take several days or more for any chemical change to happen since the dissolution rate of the coral will vary. just measure the pH to begin with since this is probably the easiest means to determine whether a change is taking place. afterwards you can directly measure the other parameters you're interested in.