First post on the forum after lurking for the past few months. Really impressed with the knowledge base around here: I was about to drop some big coin to replace my water softner before finding this forum. After reading through several posts, I decided I may just need to replace the resin. And it worked!... but... (scroll to the bottom for the question without the background information).

This is a Culligan Medalist series softner: .75 ft^3. It was in the house when I bought it as a repo that sat empty for nearly a year. The softner was on a really nasty well with a lot of sulfer and iron before I got the house. I tied in to city water which has a total hardness of 18 grains (13 grains + the "others") , 200ppm. The softner was not advancing through the regen cycles when I hooked it up. Having the control unit rebuilt took care of that: the guy at Culligan said needing a rebuild would be expected given the well water the house use to be on. I also cleaned the brine tank and cleaned out the resin tank and replaced the original resin with new resin (got the 10% cross-linked).

There are two adults in the house. We don't use much water: one shower apiece each morning and a couple of bathroom stops. Usually run the dishwasher once a week (sometimes twice); and do 2-4 loads of laundry each weekend. The control unit was set to the following specs by the guy at Culligan:

18 grains hardness
10# salt
10 min backwash time
regen every 750 gallons

The water is soft after a regen cycle; but gets notably hard again before the next regen cycle. I set it down to regen at 600 gallons this weekend; but wondered if that kind of thought is the correct answer.

Given the above specs and info, is it reasonable to expect to go 750 gallons between regen cycles without noticing the water is harder?

The only thing I can think of that might be muddying the waters a bit is that we do have a whole-house humidifier on the furnace that is fed hot water via a small line like would feed a fridge ice maker. It's on a humidistat; so it's only running when the indoor humidity drops below 35%... but ends up running a good part of the day this time of year. I wondered if the small water line didn't allow enough flow to register on the softner. It's max output is 40 gallon/day; so by the end of the week it could potentially be adding quite a bit of extra water usage if it's not being detected. Thanks in advance for the help!