I also use 50/50 RO to city for most ales 75/25 for beers requiring finesse. I still add gypsum to my pale ale to get that hop bite and mineral flavor. Generally I also use a small amount of Phosphoric acid in the sparge water as well. RO water alone can cause problems as it has little buffering power. You need to be aware of your ph throughout. If your adjusting RO with Phosphoric watch out a little goes a long way, and as soon as you add a bit of city water depending on your water profile things change quite a bit. Make sure you have some kind of carbon filter on your city supply or pre boil it. RO can also wreak havoc on heating elements and piping because it will actually pull minerals out of the pipe.
"You are what you is." FZ