"Not so hard" water

[mxw128]

Regarding water hardness:  The water that comes out of my tap tests as "low" for calcium hardness (between 50 and 120 ppm according to the test strips)  I don't have a water softner, it's just the way it is...  I know that hard water can be an issue with mineral deposits, but what problem (if any) might low(er) hardness cause?  Is there anything I should add to raise it?

[HotTubMan]

You should boost your calcium level to the 150-200 ppm range.

Water that is low in calcium can be aggressive and do damage.

Water that is low in calcium can foam very easily. Remember the sales pitch when they sold you the water softener, remember how they told you how little soap you will use?

Its all about BALANCE

[HotTubMan]

 I know that hard water can be an issue with mineral deposits,

These deposits would most likely occur on your heater. This can be prevented through proper water balance and the use of a sequestrant (aka Stain & Scale remover/control type product)

[mxw128]

Remember the sales pitch when they sold you the water softener, remember how they told you how little soap you will use?

I don't have a water softener.  

What can I add to the tub to raise the calcium hardness?

[r100rs]

You can buy a bottle of "Calcium booster". I believe Leisure Spas markets it.  Check with your dealer or go online.  Also check other dealers if they are closer.

r100rs