why do fish tanks need filters but ocean fish don’t require filters?

Question

why do fish tanks need filters but ocean fish don’t require filters?

In: 1

Answer 1

The ocean has plenty of filters. Everything is food for something in the ocean. Fish waste is food for smaller fishes, plants, corals, mollusks, shrimp whatever. Water cycle keeps minerals constantly coming in and rejuvenates o2 levels. Algae growth is kept in check by the huge number of animals that eat it. Everything is constantly recycled in the ocean, but a lack of biodiversity in 90% of aquarium tanks means that human intervention is required to do the job that life and water cycle does in the ocean.