Yes you need a mixed bed, and careful of what "calcite and corrosex" you use; there are huge differences in them from one brand/type to another.
Although I agree with Bob on the prefilter, they are useless, I say that with an upflow model you will over correct the pH at first and then it probably won't be raising your pH to 7.0 during peak demand flow rates. After over correcting stops (the corrosex will be used up), the calcite alone won't be capable of raising the pH to 7.0.
Sorry Bob, personally, they should outlaw upflow AN filters. The bottom basket clogging up is why the need for prefiltering. A blocked bottom basket shuts off your water eventually, before that it makes live miserable. And the mineral gets dirty which reduces flow and the dirt can not be removed because there is no way other than replacing the mineral. And unless the tank is a TDH (top dome hole) type, you have to remove the filter from the plumbing to add new mineral and there's no way to backwash the dust out or the old mineral of dirt, so you're adding new on top of dirty... not good. About the only good in an upflow AN filter is the purchase price, but the cost is always higher than a correctly sized backwashed model. Cost being purchase price + maintenance + all damage done to plumbing and fixtures if the acid neutralizing doesn't work right...
I've treated many wells with even lower pH than your water has. I've sold one upflow many years ago, and never again. All filters and softeners have a specific service flow rate (SFR), totally dependent on the volume of mineral or resin only. The volume dictates the size of the tank used, the size of the tank dictates the control valve that can be used. The control valve has to be capable of backwashing the volume of mineral AND the well water system must be capable of delivering the gpm and pressure required to do that.
That's why you don't see larger than 2.0 cuft AN filters; the mineral is too heavy for most well water systems to backwash it properly. And since all waters contain invisible dirt, backwashing is the best way to go, and IMO the only way to go if you want to protect the plumbing and fixtures and be much more service free as far as the equipment goes. Also, all mineral manufacturers give the OEM/dealer the backwash requirements, if upflow were to be used, why would they give backwash requirements? Why do you see very few dealers selling upflow, OR why do you see the majority of dealers selling backwashed...? Could it be we don't want unsatisfactory results and lawsuits?
All backwashed models have a settle rinse, to compact the bed. Upflow expands the bed every time you run water in the house... That does not allow proper time for the neutralizing of acidic water. The need to backwash is to prevent channeling which prevents the mineral from raising the pH.
IMO, a 1.0 cuft is too small for a family of four, and your pH BUT the SFR of the filter is way lower than a 2.5 or larger house will require.
Gary
Quality Water Associates