Cal Hypo Explained: The Good, The Bad & The Calcium

What if your “quick shock” could bleach a liner, stain a step, or even trigger an explosive reaction in your feeder? We take a hard, practical look at calcium hypochlorite—cal hypo—and share how pros use it for powerful oxidation without piling on cyanuric acid. From real-world dosing to regional water chemistry, we map the choices that keep your pool clean and your surfaces safe.

We start with clarity on strength: why 73 to 78 percent cal hypo nearly matches a gallon of 12.5 percent liquid chlorine by output, and when that field rule of thumb—one pound to one gallon—makes sense. Then we get into the must-know risks: never mix cal hypo with trichlor or dichlor, don’t drop it on vinyl or colored fiberglass, and watch for copper-driven black stains on plaster when oxidation hits metals. You’ll learn how much calcium cal hypo adds, why pH temporarily rises, and how to think about LSI and regional hardness whether you’re in Southern California’s high-calcium zones or softer-water parts of Florida and Texas.

Because cal hypo is unstabilized chlorine, we set clear CYA targets—50 to 70 ppm—to protect it from UV burn-off. We compare cal hypo tablets to trichlor tabs, explain why they’re not one-to-one replacements, and detail the flow and temperature realities that make tabs dissolve too fast in hot markets. You’ll hear practical tactics: when to feed through the skimmer during a long run cycle, how to place broken tabs on stubborn algae in pebble or on step corners, and when to stage 25 or 50 pound buckets at the pad for easy, consistent care without hauling heavy jugs.

• comparing cal hypo strength to 12.5 percent liquid chlorine
• why mixing with trichlor or dichlor is dangerous
• calcium increase, pH impact, and regional hardness
• safe application by surface: vinyl, fiberglass, plaster, pebble
• metals and black staining risk with strong oxidation
• unstabilized chlorine strategy and ideal CYA levels
• cal hypo tablets vs trichlor tablets, feeders, and heat effects
• pro tips for algae on steps and in pebble crevices
• stocking, staging buck

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