Water taken directly from the tap may contain harmful compounds that we can easily eliminate by installing a RO filter in the shower or sink, which effectively separates impurities from chemically pure water. The osmotic filter for aquariums, whose final product is RO water, removes both mechanical impurities and those invisible to the naked eye, as well as chemical compounds such as chlorine. This element is an inseparable component of tap water, responsible for disinfection. The task of the RO filter is to protect fish and aquarium plants from its harmful effects. Using cartridges is essential for the RO filter for the aquarium and remembering to replace them. If we own a marine aquarium, the device must be equipped with demineralizing resin, which will additionally remove silicates and carbon dioxide from the water. A marine aquarium is considered much more demanding than a freshwater one, which is why it is so important to always use water from the RO filter for water changes.