SpaGuard® Calcium Hardness Increaser – 12 oz Granular Formula

SpaGuard® Calcium Hardness Increaser is a granular treatment that raises calcium hardness when it drops too low. Low calcium hardness makes spa water "aggressive," meaning it pulls calcium out of anything it can — grout, metal fittings, heater elements — which can lead to pitting, corrosion, and premature equipment wear over time.

The formula is built around calcium chloride (roughly 75–97%) along with small amounts of sodium chloride and potassium chloride, and it dissolves quickly once added to the water. One tablespoon per 100 gallons raises calcium hardness by approximately 25 ppm, so you can dial in the exact level your spa needs — most manufacturers recommend keeping hardness between 150–250 ppm for spas. This 12 oz container works with any sanitizer system, including chlorine, bromine, ozone, salt, and mineral setups.

Because the reaction is exothermic, always add the product to water rather than water to the product, and avoid direct skin or eye contact while handling it. Keeping calcium hardness in range is one of the simplest ways to protect your spa's shell, plumbing, and heating components long-term.

Low calcium hardness often shows up before you'd expect it to: water may foam more easily, metal fittings and heater elements can develop a dull or pitted look, and vinyl or acrylic surfaces can feel slightly rough as the water pulls calcium out of anything it touches. Catching these signs early and correcting hardness based on an actual test kit reading is far cheaper than replacing corroded equipment later, which is why most spa manufacturers list calcium hardness as a routine weekly or biweekly test alongside pH and sanitizer.