On any other aquarium board, it would be blasphemy to even ask this question... How many people have dropped filtering their top off water since they have gone to using a scrubber? And, have you observed any negative effects?
I never really understood the whole RO/DI thing. I hear (smart, successful) people saying that you can't have *any* TDS in your make up water, not even 1 PPM. But then they throw 5-10 cubes of frozen food in their tank daily (along with amino acids, "coral food", and all sorts of other stuff). It seems to me that any contaminants in the source water would likely be irrelevant once you factor in feeding. Is using RO/DI a herd mentality thing like using skimmers? I suppose if you have really hard well water or something, maybe you need to do something more, but it seems to me that with decent city water, adding a few drops of Prime to take out the chlorine should be all you really need to do.
That said, I use a DI filter and have continued to since I started using a scrubber, mostly due to fear that maybe (smart, successful) people are right about the whole RO/DI thing, but also due to the fact that I have extra DI cartridges that I might as well use up. But, when those are done, I'm wondering if I should drop filtering and just let the scrubber take are of the small amount of anything that gets in the system from the top off water.