My well water passed through a large main line filter. Then to the water softener and then the ro, for the tank, drinking and fridge/icemaker water.
BUT !!!!! Here the mistake I made which led to down sizing and selling my 225g. The ro does not remove any excessive alkalinity. DUH ! I never knew that, kind of naive I guess about ro units. Got spoiled in Thompson with our good water.
Took me forever to figure our what kept screwing up my alk. and preventing me from keeping sps corals. Here all I needed was a DI on the backend of my ro unit. Geez, now someone tells me.
So thats my advice for filtration of well water and the only way I would ever use it for my systems. FWIW, of course.