IMO, DI is overkill, a RO unit will work just fine. You can connect them permanently or have a temporary connection. I use straight RO for my tanks, some add stuff to it. I see no need to add stuff plus I am using 300 gallons a week. There are several types available on ebay, just make sure you are getting a quality unit. I got mine at Premium Aquatics because they are local and I could touchy feely before I bought. I like the unit I have, pics in my links below.....DCI've been thinking of purchasing one of these as of late because of the tap water in my apartment. Can anyone explain how they work? Do these permanently plumb into existing faucets, or do you connect a hose to them, then transfer water into a water holding container to reconstitute it. The tap water is horrible, has a funny smell, and a horrible taste to it. I beleive it is ran through a water softener as my gH measures <1 degrees, and my kH measures 5.6 degrees. What brand would you recommend?