Pond fish

Inside the house we have a tropical aquarium full of interest for the fish , caves , plants , drift wood etc .. Outside our deep glass sided pond has nothing , partly due to the growth of algae that could develop .. we have floating plants , it may seem daft but has anyone got anything in their pond to give the fish some interest and to kept them mentally entertained? .. They have a large pond and are well cared for but I can’t help but think the inside snobby fish have their bread well and truly buttered compared to our Koi.. See less