I might trust Prime to clean up the tapwater....might being the operative word. Where I live they often run right up against or a bit over all the recommended EPA water safety limits and every few years have to issue an alert for pregnant women not to drink the water.
The real issue is they have a very old water plant and they don't want to spend the money to bring it up to modern standards. As a result I'd rate our water quality poor here. Prime since it not only de-chlorinates but removes things like ammonia from the water, which we have here, as I mentioned might clean the tap water up enough to use but I think I'd rather have the result tested before actually using it.
RO water is a 15-20 min trip to get but I already have four 6 gallon water jugs to pick it up in.
Im getting both the RO water and current aquarium water tested at the store today as I know pH alone is telling me very little about whats going on with my water. I suspect the rise is from the water conditioner that the Eco-Complete is packaged in as well as the RO water leaching minerals out of the substrate. It will really take a GH test as well as some specific mineral tests to really tell me what I need to know.