Those bright reds are NO3 limitation AND lots of bright light. I doubt you need R/O water, usually tap water doesn't have a lot of nitrates in it unless you're in an area with a lot of agriculture. You don't really need to get rid of nitrogen in the water, as long as you don't actively dose it your plants will eventually use all available nitrogen in the water column.
I suggest using Osmocote+ balls around all the plants that do want nitrates (baby tears, lysimacchia nummularia, ludwigia) and then using a liquid fertilizer without nitrates such as ADA Brighty K, Tropica Premium Nutrition, APT Zero, or Seachem Flourish. You can also use Seachem Flourish root tabs around the red rotalas since it doesn't contain nitrogen.
Is your photoperiod still only 4 hours? You could try increasing that as well. Turning red is a light stress response, so really blasting your tank with light is sure to help. It will probably also mean more algae on your hardscape but that can be controlled by spot treating with excel/ H2O2 and a wire bristle brush.
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