Hey there,
I am definitely not nearly as experienced as Bernd with different Paros but I would leave the pH as it is for now . Even thought I have my fish under more extreme conditions, it is just because it is simple for me to prepare such water. If you want to have more stable and lower pH you can try to combine the alder cones with Terminalia catapa leaves extract and or oak leaves (combination of substances is usually more powerful) or if you find out later that you need extremely low pH, you can use peat (but you have to work with the ion exchange power of it 🙂 or some acid. If there is some tap water in the tank, you can still continue with the pure RO water changes and make the conductivity lower as the concentration of unwanted ions could still be a little too high.