The limiting factor will be the DO (day override which sets the maximum time between regens) number. If you had an Iron+H2S backwashing iron filter first, that would let your softener go much longer between regenerations. Maybe you could get by with more than 7 now. If you have a sulfur (H2S) smell, that would be a strong additional reason to add that Iron+H2S backwashing iron filter, which would let you move your DO to much longer.
A Res Care or Res-Up feeder would feed a continuous dose of phosphoric acid into the brine tank to help deal with the iron. The special iron-handling salts have citric acid and maybe more in the salt to help dealing with the iron. So how long can you go with DO while using these measures? I don't know. I don't think there is a hard prescription.
If you search this softener forum for "iron out" you will find older discussions that you may find of interest.
System info (not programmed)
salt lb/cuft = 6 ; A choice ( efficiency vs capacity)
BLFC = 0.5 ; Brine Refill rate GPM
cubic ft resin = 1.5 ; ft3 resin = (nominal grains)/32,000
Raw hardness = 17 ; includs iron compensation
People = 1 ; gallons affects reserve calc
Estimated gal/day = 60 ; 60 gal per person typical calc
Estimated days/regen = 29.4 ; Computed days ignoring reserve and DO
Fleck 5600SXT Settings:
DF = Gal ; Units
VT = dF1b ; Downflw/Upflw, Single Backwash
CT = Fd ; Meter Delayed regen trigger
NT = 1 ; Number of tanks
C = 30.0 ; capacity in 1000 grains
H = 17 ; Hardness-- compensate if needed
RS = rc ; rc says use gallons vs percent
RC = 60 ; Reserve capacity gallons
DO = 7 ; Day Override (due to iron)
RT = 2:00 ; Regen time (default 2 AM)
BW = 5 ; Backwash (minutes)
Bd = 60 ; Brine draw minutes
RR = 5 ; Rapid Rinse minutes
BF = 6 ; Brine fill minutes
FM = ___; flow meter, make note of what is there
