If the pH of your RO water is too high, sphagnum peat can lower it. To raise the pH, a very weak solution of a strong base like lye would be a good choice. Use caution with concentrated solutions of strong bases and acids. RO water is simple to understand. It is just tap water most of whose salts have been removed.
RO water is simple to manage.
RO water is expensive to start. RO produces waste water you must dispose of. But remember, the waste water is very like your tap water. So it can be used in applications where your tap water works well. Examples might include clothes washing, plant or lawn watering, toilet flushing.