This is all borderline:

Your lab is showing slightly less than 1 grain per gallon hardness - which is the definition of soft water. Your plumber is showing 2 grains - not very different from lab and within the limits of accuracy of his test kit. Neither reading would prompt me to install a softener. I understand that you believe that once the neutralizer has been added, the hardness will go up - thus the softener.

The lab is testing the PH at 6.5 - which is the bottom recommended by the EPA (under 6.5 calls for treatment). The plumber is measuring 6 - but again not very different and within the limits of his test kit.

I think you could be fine not treating this water.

Keep in mind that any treatment that you do adds in more maintenance and such and so using a minimal amount of treatment has a lot of advantages.

Here's what I would do: I'd completely plumb this so that I had the option of adding a neutralizer and softener - so with the bypass loops, drains, power etc. - but I'd hold off on installing anything.

If you add a neutralizer later, I'd check the hardness after that's in service and see where it is.

If you need to change the PH of the water - it's not going to be by much. Ditto with the water softener.

@jakethewonderdog

Thank you so much for your reply and input. It's interesting because last night my husband and I were talking about not doing anything - because the house is 50 years old. There have been a few places when remodeling the bathrooms where there was blue corrosion all over the pipes. But the remaining copper *seems* to look okay - the plumber cut into one at the sink and he said the insides looked good.

Our concern is the possibility of messing up a new tankless (gas) water heater that we are having installed if the water is acidic. Knowing we are installing a tankless system on well water, would you still leave it for now but plumb it (primarily the discharge pipe is what needs to be plumbed in before we sheetrock I think?) in case we add it later?

The units will sit in an unfinished "mechanical room"

Check with your water heater install manual for the acceptable water pH limits. For example, the Rheem tankless shows the range of 6.5-8.5 as acceptable. Use the lab results rather than the plumber results.

At two grains per gallon or less, I would not be concerned about the tankless water heater. If you had hard water, my answer would be different. Be sue that the tankless heater is installed with a set of service valves so that cleaning it is relatively easy - which is a best practice no matter what the hardness level.

Again, I would go ahead and plumb everything so you have that option later - so you just have what is known as a softener loop, but no softener. Generally, the softened water excludes outdoor faucets and possibly the cold water in the kitchen.

BTW: With a well, you should test your water every couple of years for contaminates - since nobody else is doing that for you. Things can change: these might be farm chemicals, feedlot runoff, an industrial plume that has migrated, etc. You can get the pH confirmed to be 6.5 or above when you do that.