an apparatus used to remove ions from a solution; a common variant contains a mixture of cation exchange resin in the acid form and anion exchange resin in the hydroxyl form inside a replaceable cartridge; ions in aqueous solution are exchanged for the elements of water by passing the solution through the mixed resin.

A device that filters municipal tap water prior to aquarium use.

A filtration device used to purify tap water before it is introduced into the aquarium. They are normally composed of many chemical and mechanical filtration media.