Filter Bags are needed to remove excess organic and inorganic suspension from the water. Most of this suspension is Detritus.
Detritus is organic debris, dead and Live Bacteria.
In small amounts, detritus is a necessary resource to feed the Microbiology of your Aquarium.
If a new Aquarium System runs out of Detritus, there will be problems with the nutrition of beneficial microorganisms and Bacteria. Therefore, it is necessary to ensure that the necessary supply of Detritus appears at the initial stage.
That is, if when you start a new Aquarium System you are fine with the amount of Detritus and ORP, you do not need to install Filter Bags.
Sometimes in an Aquarium with a large amount of Fish, biological processes are disturbed and a large amount of Detritus accumulates, Nitrate and Phosphate increase. In this case Filter Bags or Fleece Filter should be used. Filter Bags should be washed at least once a week.
If your Aquarium's Biological System is perfectly balanced, Mechanical Filtration is not necessary. Living organisms in a Marine Aquarium will completely absorb all food and organic matter.