Where does the 8.5 gpm come from?
And how do you know you only need a 1.0 cuft? That will give you a SFR of about 4 gpm and a 1 bath house can exceed that very easily.
You would be better off with a chlorination system but I don't like using the pressure tank as part of the retention. I don't like solution feeders either. A dry pellet chlorinator and a special mixing tank is the best choice.