"Director, why don't we keep some fish in the hippopotamus exhibit? It would look so beautiful to see schools of fish swimming together with the hippos."
Fang Ye smiled and said, "Well, keeping some fish isn't a bad idea, and they could help clean the water quality.
But what hippos love to do most is to defecate in their territory, and the speed at which the fish clean couldn't possibly keep up with the speed at which they poop. If we kept fish, we couldn't change the water every day.
Especially in the summer, when bacteria and algae reproduce even faster, the water quality deteriorates more quickly. Maybe after a week, all the fish would be dead, and we can't treat them as disposable goods.