You can increase CH with calcium chloride, which is sold as a deicer, and by pool stores, or calcium chloride dihydrate, which pool stores sell to increase calcium.
In some parts of the country (the southwest, for example), high water hardness causes CH to naturally increase in pools when there is more evaporation than precipitation.
Beware of buying ice melters to increase CH. Most of the cheaper ones are salt-based. Some will increase your salt as well as your Calcium. Check the MSDS of non-pool products to find the ingredients.
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