Why Choose Hot Tub Things?
Authentic & Genuine Products: Never knockoffs or expired inventory
Competitive Pricing: Best value for premium spa care products
Expert Customer Support: Our team knows hot tubs inside and out
Great Everyday Value: Strong fit and quality without OEM pricing
Satisfaction Guaranteed: Thousands of happy spa owners nationwide
Fast Free Shipping: Free shipping on orders $100+ (see terms)
Available in stock (117)
Hot Tub Things® Calcium Increaser – Spa Hardness Booster
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Precision liquid formula raises spa water calcium hardness efficiently, helping prevent corrosive “hungry” water that can damage heaters, plumbing, and metallic parts.
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Ideal for weekly use or fresh fills in spas with low or softened water, restoring balance without overshooting to scale-forming levels.
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Helps minimize foam, cloudiness, and sanitizer demand by maintaining stable hardness—essential for optimal sanitizer effectiveness.
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Compatible with all hot tub sanitizer types—including chlorine, bromine, saltwater, and mineral systems—simplifying your chemical routine.
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Convenient 32 oz bottle with marked dosing lines makes it easy to add precise amounts based on spa volume.
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Backed by Hot Tub Things’ quality assurance, safety-tested for spa use and formulated without harsh fillers—trusted by professionals and DIYers.