Goldfish boy ive seen you around on the planted side. Im going to follow your build as i want to make this jump in the future. Will be a good learning curve for me too.
Remember in a planted tank your trying to keep a constant level of nitrates, phosphates and other elements for good plant growth.
In a saltwater tank you want absolutely 0 of these things. I believe corals need certain micro nutrients that we use in the planted side but im sure the salty guys will let you know about that.
unit takes your tap water and passes it through a number of filters, a reverse osmosis membrane and a de ionisation resin. The water comes out 'pure'. It contains no chemicals, no dissolved solids (such as copper, calcium or iron) and no bacteria. It gives you a perfect base for your aquarium. You can then add the nutrients that you need and monitor them to keep it a constant.
If your ever on the planted side i have a progression thread. About halfway through the thread i purchased a RO
unit and set it up. It may be worth a read for you if your interested