Your ratio will depend on the hardness of your source and RO. I try to get my tds down to 60 ppm or so. At least below 80. I don't worry about pH and since I'm on a well with high KH, I'm sure it's close to 8. The fish don't care if they're used to it. Folks will sometimes give a mild dose of formalin (Rid-Ich) to a tank when a pair is looking to spawn, to reduce fungus. I've done that but do like to change the water again before the spawn. Just my thoughts.
Steve