Why did aquarium keeping become more successful after scientists understood oxygen relationships between plants and animals?

Aquarium keeping became more successful in the mid-19th century because the discovery of the respiratory relationship between plants and animals allowed for the creation of "balanced aquariums."

Scientists realized that aquatic plants and animals could sustain one another in a closed system: animals consume oxygen and release carbon dioxide, while plants—under sufficient light—consume carbon dioxide and release oxygen through photosynthesis. Additionally, the waste products produced by fish serve as nutrients for the plants. When these processes are balanced, the environment remains stable, which enabled the development of the modern aquarium as a vessel for keeping aquatic animals alongside plants.12