I feel like my plant liked the transition from tap water to RO water. 150 ppms of chlorine, salts, and waste vs 30-50 ppms... the lower the ppms the less pH down it seems to take to adjust the pH.
Learning the science behind how plant use nutrients and how hydrogen effects nutrients would be something useful to learn to have a full understanding of ppms, pH, and plant deficiencies and toxicities. Perhaps learning this will teach you how the RO filter will benefit your plants.
Otherwise hopefully someone with this knowledge will chime in
I personally believe that the chlorine weakens and kills beneficial bacteria but surely it also has a direct negative impact on the roots as well. The unwanted salts and solids in water also will build up over time which will hinder the flow of oxygen around the rootzone.