Hello,
I would ask first, what kind of feed? Maybe trying to get a feed that has a bit lower protein content may help, but I know with the other one being smaller that you may want to keep a higher protein for it-difficult huh?
Medicated chick starter is NOT good for ducks. The ducks ingest much more food than chicks, and can get too much medication. Also, chick starter does not contain enough niacin, which is VERY important for a growing duck. Do a google of niacin (a B vitamin) to see whatit is neccessary for. Also, if I remember correctly, chick starter has a higher protein amount that may cause growth too fast. The reccomended food is waterfowl starter-but thats hard to find. The next choice is non-medicated gamebird starter.
Info on niacin-B3:
Niacin assists in the functioning of the digestive system, skin, and nerves. It is also important for the conversion of food to energy.
Vitamin B3 - niacin, niacinamide, nicotinic acid - information page
Niacin also called nicotinic acid, niacinamide or nicotinic acid and referred to as vitamin B 3, which can be manufactured by the body. Niacin is derived from two compounds - nicotinic acid and niacinamide.
Vitamin B3 is required for cell respiration, helps in the release of energy and metabolism of carbohydrates, fats, and proteins, proper circulation and healthy skin, functioning of the nervous system, and normal secretion of bile and stomach fluids.
A deficiency may cause pellagra, the classic niacin deficiency disease, and is characterized by bilateral dermatitis, diarrhea, and dementia.
Best wishes!