I'm thinking about eventually getting a Reverse Osmosis unit. I want it to mix with my tap water in my 75 gallon freshwater tank; the tap water is at least 8.6 pH and 10 dGH. I want to get the water in my tank down to 6.5-6.9 pH (there is some bogwood in my tank too, which helps slightly). However, I'm not sure what to look for in a RO unit, I have no idea what is necessary, desirable, or just fancy. Could someone please help me? Also, is there any way I can get a rough idea of what parts of RO water I'd need per part of tap water? I'm very new to the idea of an RO unit.