Hardness is a mixture of various minerals dissolved in the water, usually containing Calcium & magnesium...just not the Ca & Mg salts we *want *in our salt water in the tank; what 'hardness' is varies from place to place.Oh, probably a silly question but how does an ro/di unit affect the waters hardness or does it?
Reverse osmosis (the RO in RO/DI) is the process of forcing a solvent (in this case water part of your hard water) from a region of high solute concentration (lots of dissolved minerals) through a semipermeable membrane to a region of low solute concentration by applying a pressure in excess of the osmotic pressure ...so at my house I have a booster pump on my RO/DI unit to make this happen.
Deionized water, also known as demineralized water (the DI on your RO/DI unit), is water that has had its mineral ions removed, such as cations like sodium, calcium, iron, and copper, and anions such as chloride and sulfate. Deionization is a chemical process that uses specially manufactured ion-exchange resins which exchange hydrogen ion and hydroxide ion for dissolved minerals, which then recombine to form water (definitions are off of WikiPedia...they do a great job!).
Itsa 2 step process, the 'hardness' (= a mixture of various minerals in your water) is removed, then more is removed which makes for very pure water.
Then we dump a bunch of salt in it ! Crazy, huh!?!:der::der: