Oversizing a water softener (semi-commercial)

[Westinghouse]

I know there are articles here for oversizing softeners but I have a special situation...
I have an Estate that has a large well that produces a minimum of 75 gpm with a 2" pipe going to the rest of the property.
The pipe goes from well to the carriage house - which has 3 people there. Then it continues on to the main "mansion". This large house has 14 bathrooms, 12 bedrooms. Currently I only have 6 people in there. In the near future, I will turn my house into a B&B and let's just say when open I will have 12-15 people at any one point (and up to 20 people when full). There will be some months where I will have a minimum amount of people - my core 9 people for the whole property

My water hardness is at 12 grains and I have 2mg/l of iron and 2mg/l of sulphur (bacterial), and I have a Manganese issue (unknown amount). While I can set up a small system, this is getting a bit out of my comfort zone so I called in a water company and they recommended doing a Chlorinator, carbon filter to a softener. I originally picked up a dual 3 cu ft. tank system for the softener a couple years ago (not installed) but they told me it's way too small (even if I pump treated water to a 1000 gallon holding tank to await demand). Large systems that will handle 2" supply lines are quite expensive so I was very happy when I found a cheap dual 10 cu ft. tanks with the valves that have 2" fittings (he says that it is set for 300,000 grains). Now after re-thinking this, this MIGHT be WAAAY too large for property - especially in the months when I have minimal occupation in the houses.

I have the pressure and I have the flow to support these big tanks. However if I don't have the water demand during the low months, will extending the regeneration time be detrimental? I'm hoping that I could get away with keeping the 10cu/ft tanks and fill with new resin. What are your thoughts??

 

[Reach4]

My water hardness is at 12 grains and I have 2mg/l of iron and 2mg/l of sulphur (bacterial), and I have a Manganese issue (unknown amount). While I can set up a small system, this is getting a bit out of my comfort zone so I called in a water company and they recommended doing a Chlorinator, carbon filter to a softener.

You want to avoid oversizing if the softener is having to remove the iron. However with your chlorinator, followed ideally by a contact+settling tank, then followed by the carbon, the iron should be removed by the time it hits the softener.

So with the iron and manganese gone, you still want to regen at least every 30 days.

I have not analyzed your numbers, but I just wanted to make two points... after the carbon there should not be iron and Mn, and that you should want a contact/settling tank after the chlorine injector. It should have a bottom "blow-off" port to dump the sediment including rust.