Hang-on-back filtration provides ongoing water purification for your aquarium through chemical, mechanical and biological filtration. Additionally, the use of coconut carbon media versus traditional coal carbon provides a more desirable form of chemical filtration. Choosing the right size aquarium filter can be a challenge. For most aquatic life, we recommend finding a filter that will turn the volume of your aquarium water an average of 6 times per hour. However, this will vary for slow swimmers that need less flow or for marine aquariums, which typically require higher flow.