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Types of Pool Shock Compared: Cal-Hypo, Dichlor, Bleach, and MPS

Shocking a pool is the process of adding a large dose of oxidizing chemicals to destroy chloramines, eliminate algae spores, and clear cloudiness. However, walking down the chemical aisle at a pool store can be overwhelming. Bags and jugs labeled shock contain four entirely different chemical compounds, each with unique advantages and potential side effects. Choosing the wrong shock can inadvertently spike your calcium or drive your cyanuric acid into chlorine lock. This guide breaks down all four types of pool shock, with dosing help from our pool shock calculator and pool chlorine calculator.

11 min read, updated September 2026

Key takeaways

  • Cal-Hypo (calcium hypochlorite) is potent (65% to 73% chlorine) but adds 7 ppm of calcium for every 10 ppm of free chlorine.
  • Dichlor shock granules dissolve rapidly but add 9 ppm of cyanuric acid for every 10 ppm of free chlorine.
  • Liquid chlorine (sodium hypochlorite) adds zero calcium and zero stabilizer, making it ideal for routine shocking.
  • Non-chlorine shock (potassium peroxymonosulfate) oxidizes organic waste without adding chlorine, allowing swimming in 15 minutes.

The Four Main Types of Pool Shock

All pool shocks are designed to oxidize organic contaminants, but they use different chemical compounds to accomplish that goal:

Chemical Attributes and Byproducts of Common Pool Shocks

Shock TypeChemical CompoundAvailable ChlorineByproduct Added to WaterBest Use Case
Cal-HypoCalcium Hypochlorite65% to 73%+7 ppm Calcium Hardness per 10 ppm FCSoft water pools; Vinyl liners (pre-dissolved)
DichlorSodium Dichloroisocyanurate55% to 62%+9 ppm Cyanuric Acid per 10 ppm FCHot tubs; Pools with zero CYA
Liquid Pool ShockSodium Hypochlorite10% to 12.5%Harmless table salt (0 calcium, 0 CYA)Routine weekly shock; Algae eradication
Non-Chlorine ShockPotassium Monopersulfate (MPS)0% (Non-sanitizer)Sulfate residuals (0 chlorine added)Indoor pools; Fast swim turnaround in spas

Cal-Hypo (Calcium Hypochlorite): The High-Strength Classic

Cal-hypo is the most widely sold granular shock in the world. It delivers strong killing power at 65 to 73 percent available chlorine by weight. However, for every 10 ppm of free chlorine added from cal-hypo, you add approximately 7 ppm of calcium hardness to your water.

If your pool already has high calcium hardness (over 350 to 400 ppm from hard tap water), using cal-hypo will cause rapid scaling on pool tiles and precipitate out as cloudiness. Additionally, undissolved cal-hypo granules that sink to the floor will bleach white spots onto vinyl liners. Always pre-dissolve cal-hypo in a bucket of pool water before adding.

Dichlor: Fast Dissolving with a Stabilizer Trap

Dichlor granules dissolve almost instantly in cold water and have a nearly neutral pH of 6.8 to 7.0, making them popular for quick pool treatments. However, dichlor contains nearly 50 percent cyanuric acid by weight. Dosing a pool with dichlor shock will skyrocket your stabilizer levels within weeks, triggering chlorine lock. Dichlor should only be used in fresh water fills with zero stabilizer, or in hot tubs where water is replaced quarterly.

Liquid Chlorine: The Zero-Byproduct Workhorse

Liquid chlorine (sodium hypochlorite) is the preferred shock of professional service technicians. Because it contains no calcium and no cyanuric acid, you can add massive shock doses during green pool cleanup without worrying about side effects. It mixes into the water instantaneously with zero dissolving required. Calculate liquid shock volume with our pool shock calculator.

Non-Chlorine Shock (MPS): Rapid Oxidation Without Chlorine

Non-chlorine shock (potassium peroxymonosulfate) is not a sanitizer; it does not kill living algae or bacteria. Instead, it is an aggressive chemical oxidizer that consumes bather oils, cosmetics, and organic waste, preventing them from combining with free chlorine. Its biggest advantage is convenience: swimmers can safely re-enter the pool or hot tub just 15 minutes after treatment. Check small-volume dosing on our spa chemical calculator.

types of pool shock FAQs

Can you mix different types of pool shock together?

Never mix different dry chemicals or shock types together in a bucket or feeder. Mixing cal-hypo with dichlor, trichlor, or acid produces an immediate violent chemical reaction, intense heat, toxic gas clouds, and explosive fire. Always add one chemical at a time directly to the pool.

When is the best time of day to shock a pool?

Always shock your pool in the evening after sunset. Ultraviolet sunlight breaks down unstabilized chlorine rapidly. Shocking at night gives the sanitizer 8 to 10 hours of darkness to oxidize contaminants at full strength.

How often should you shock a swimming pool?

Shocking on a strict weekly schedule is usually unnecessary if you maintain proper free chlorine. Shock when combined chlorine tests above 0.2 ppm, after heavy pool parties, following major rainstorms, or at the first sign of algae or water haze.

Why does pool shock cloud my water?

Cal-hypo shock temporarily clouds water because calcium precipitates when concentrated shock meets high pH. The cloudiness usually dissipates within 12 to 24 hours as the filter runs. If water remains cloudy for days, your calcium hardness or total alkalinity is too high.