Turtles and Ducks may be cute and exciting to watch, but their feces is very rich and tend to pollute water very quickly. It is also very hard to filter their feces because being so rich like “stinky gooey chocolate” that a biological filtration is needed. Sometimes you can never get enough to handle the load that is producing. Another problem is that they both eat fish, small fish usually.
I had a client that was complaining of a fin disease inflicting his koi. On examination on the fish, I pointed out to him the “diseased” fins had chunks missing that was the exact shape of the turtles beak. The turtle was biting the fins of the fish!
Ducks can easily carry disease in feces. As they feed on fish from another pond and fly into your pond and poop, this will bring disease to your water garden and effect your fish. Both Turtles and Ducks forge and dig in soil and aquatic plants for grub, which makes a mess. Another problem are ducklings, yes they are cute as a button and who wouldn’t want baby ducks swimming around in their pond, but duckling who nest in a pond are a problem. I had a friend who once allowed ducks to nest and they had a joy watching them. Then.. they leave the nest and migrate back. Which means they will nest their ducklings in the pond and the cycle will go on and on for years and years till he had so many ducks on his property, him and his wife were trying to get them out of their yard.
Our advice, don’t put ducks and turtles in your pond!
P.S. We do have some clients that have turtles and ducks, we just clean the ponds more often then usual.