Rising Calcium Hardness

Kit

Well-known member
Mar 10, 2016
197
Medford, Oregon
The CH in my 2,500-gallon in-ground spa has a tendency to creep upward over time (from about 250 to 375ppm in 3 months). I try to keep the level in the 200 - 400ppm range. Since we do not have hard water, I am curious what might be the cause. The chemistry is checked & balanced weekly & the spa has an auto cover. There is no scaling on the tile along the water line. I realize that this is not a critical issue; but I am just curious as to the cause. Thank you so much.
 

jimbethesda

Gold Supporter
Jul 2, 2018
445
Austin, TX
Do you ever put cal-hypo in? Even if your water isn’t “hard” it still likely has some calcium in it. Do you know what your calcium content of your water is? Water evaporates, but calcium doesn’t. If the replacement water has any calcium in it at all, your calcium level in your spa will increase. Slower than those with hard water, but it will still increase.
 

Kit

Well-known member
Mar 10, 2016
197
Medford, Oregon
Do you add any granulated chlorine 'shock'? Calcium Hypochlorite is the ingredient any many of those products.
I have a SWCG that does a good job of balancing my chlorine level. If slowly rising calcium hardness is my concern, I guess I don't understand how adding cal-hypo (i.e. increasing my chlorine level) will affect calcium hardness.
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
33,019
Laughlin, NV
If your calcium hardness is increasing, you are adding calcium to the water somehow. As Jim said above, either from products, like calcium hypochlorite, or from fill water to make up for evaporation.
 

jimbethesda

Gold Supporter
Jul 2, 2018
445
Austin, TX
I have a SWCG that does a good job of balancing my chlorine level. If slowly rising calcium hardness is my concern, I guess I don't understand how adding cal-hypo (i.e. increasing my chlorine level) will affect calcium hardness.
cal-hypo = calcium+chlorine

But since you said you’re not familiar cal-hypo, does that mean you didn’t put it in? Maybe it was labeled “shock” and you didn’t look at the ingreadiants.

Even if you didn’t add cal-hypo, calcium comes from your fill water.