Birds turd in my ponds all the time and fish are fine as water runs non stop all year round.
I feed my fish only the finest quality Puppy Chow, made right here in Alberta. Its super fresh and smells good too. Its made by Origen and Acana dog food. It contains no grains and my dogs love it too. My fish have been eating this food since 2003 and they are all doing great, and live outside here in Canada year round.
I like the puppy chow as it is higher in fat and my fish are never sick and I have never ever lost a KOI. The goldfish eat that food too. My koi are large and have very big mouths and it would be hard for them to eat small pebbles so I give the large koi the Large Breed Puppy chow. I don't listen to anybody try to tell me its bad. My fish are still alive and well and I think the fish food is way over priced and its sits on the self way longer than the fresh dog food. I never keep the dog food for very long as the puppies eat it too, so its always fresh which is good.
People tried to tell me it was bad to run the ponds all winter as the koi would get too cold, that's just crappy information as my koi have been outside in ice cold water since 1991 and I have never lost a single koi ever, while friends of mine who listened to the so call experts have lost many of their koi over the winter and spring months.
Just remember, if most people believe something to be true, its usually proven not to be true.... That is just a fact.