I use Seachem Alkaline Buffer to keep my pH stable. You can use Seachem Replenish or Equilibrium to re-mineralize. You'll want to monitor your KH, GH, pH regularly after you start using the RO water and these products.
Oh ok, well there are other products out there. For GH you are looking for a product with mineral salts in it like calcium chloride, magnesium chloride, potassium chloride. If you see an additive for cichlids tanks that will work as well as they usually contain mineral salts and buffers as well.
For Kh you are looking for carbonates in a product. If you don't see anything then you can use plain baking soda, or bicarbonate of soda it might be called that you use in cooking.