Soft water pros... longer service life for plumbing, appliances, and fixtures. Your tankless will thank you. Clothes last longer and are softer to wear. You'll use less soap and detergent and shampoo. It will be a long time before you fix a leaky faucet.

Based on your numbers and occupancy (including future baby for 4th person) here's my recommendation if you're on a water system. If you're on a well then things change.

1.5 cu ft (standard hi-capacity 10% cross-linked resin... NOT FINE MESH) softener using a Fleck 7000SXT or Clack WS1 control valve on your 1.25" softener loop with appropriate connectors so you don't reduce the plumbing size. Choice of brine tank with salt grid and Fleck 2310 safety float brine pickup. A bypass will come with either control valve and you'll want a top basket for the control valve AND a gravel under bed. This is the setup you want... don't let anyone talk you out of it.

Set up for efficiency it will regenerate every 8 days or so and use about one bag of salt a month.

Use those specs and shop around for a local water treatment professional. They won't program the softener correctly but I can give you the #s and you make them set it up that way.

With 15 gpg hardness and 320 TDS you should consider an under sink RO in the kitchen for drinking, cooking, and ice making water.

Thanks justalurker for the quick response!

We are also considering the rental program from Culligan (I know it is much more expensive value wise; but no need to worry about regeneration and salt refilling as Culligan will swap out the tanks for us). The sales recommends twin tanks, each with 3/4" pipe. Would that work with our 1.25" pipe?

Thanks justalurker for the quick response!

We are also considering the rental program from Culligan (I know it is much more expensive value wise; but no need to worry about regeneration and salt refilling as Culligan will swap out the tanks for us). The sales recommends twin tanks, each with 3/4" pipe. Would that work with our 1.25" pipe?

AFAIK code prohibits reducing water service size. That said, it is done but unless it would be difficult or dramatically more costly why not keep the correct size and not sacrifice any water pressure or flow? Culligan should know better.

As far as value, the softener I'm recommending can be ordered online and shipped to your house for about $575. You'd need to assemble it and have it plumbed in so add $300 for a plumber to do it and then compare that $875 with what you'll spend renting a Culligan for just one year let alone 2, 3, or 4 years. Regeneration is done at 2AM with no attention required and putting one bag of salt a month in the brine tank is pretty EZ when the softener is in the garage and not a basement.

You bought a house and aren't renting one...

Thanks again justalurker.
So this is the one you are recommending from Ohio Pure Water?

Fleck 7000SXT Electronic 1-1/4 Inch Meter On Demand Control
# 10x54 resin tank
# 1.5 cubic feet of resin
# 12 gpm service flow rate
# 2.5 gpm backwash flow rate
http://www.ohiopurewater.com/shop/customer/product.php?productid=18651&cat=632&page=1#

The price is exactly @ $575 but I am not sure about the crosslink being 10%. for the connection I will go with 1.25" brass sweat option.

Can I also use Potassium chloride for this softener to water plants?

Here is a link that might be useful: Softener from Ohio Pure Water

That is the configuration I recommend with the additions I posted...
* Fleck 2310 safety float in brine tank
* top basket for the control valve AND a gravel under bed
* standard hi-capacity 10% cross-linked resin

Don't order online... call on the phone and tell them what you want and don't get talked out of anything and don't let them charge you more.

KCl can be used in any ion exchange softener but the salt dose will need to be changed slightly. KCl has gotten very expensive so you may not want to go that route. My wife is having great success watering her house plants with NaCl softened water with no bad effects.