Ultimate Guide to Pool Shock

Welcome back, students of pool! Today we tackle a shocking subject, in the following discussion about pool shock treatments.

What is shocking the pool? For the unfamiliar, the noun 'shock' refers to an oxidizer used for sanitizing and disinfection of pool water. The verb 'shocking' the pool is the act of adding granular pool shock to super-chlorinate the pool.

In small doses, pool shock can be used to quickly raise chlorine levels, spot treat a small algae colony or remove organic stains on concrete pools. In larger doses, pool shock will restore green pools, break apart chloramine bonds, and kill bacteria.

As a Complete Guide to Pool Shock, today's lesson plan will compare the types of pool shock available, their pros and cons, and application and dosage information. But first...

Why Shock a Pool? Raising the chlorine level 10x-30x normal levels, or using non-chlorine shock oxidizer, can accomplish many things simultaneously.

  • Removes visible algae in the pool.
  • Removes invisible bacteria in the pool.
  • Removes chloramines and other disinfection byproducts.
  • Removes cloudy water by oxidizing suspended particles.
  • Removes organic and inorganic contaminants.
  • Maintains healthy, sanitary pool water.

When to Shock a Pool? The time of day matters, and you want to be consistent. Regular pool water oxidation improves water appearance, quality and sanitation.

  • Shock the pool when the sun is not shining on the pool; early or late in the day.
  • Shock as needed to correct water conditions, or every 2-4 weeks.

How to Shock a Pool? There are some techniques to proper pool shocking; in addition to the tips below, consult the pool shock label for use and precautions.

  • Clean the pool before shocking, to remove leaves or debris.
  • Lower the pH level to 7.2, to increase pool shock potency.
  • Sprinkle shock into pool, or broadcast across the surface.
  • Vinyl pools should pre-dissolve in a 5-gal bucket of water.
  • Run the filter and brush the pool afterwards to disperse.
  • Use the entire bag at once; clean up any spills quickly.


Calcium Hypochlorite

Cal Hypo pool shock products shown

The most popular pool shock, beloved for the low cost, high percentage of available chlorine, and stable pH. Cal Hypo pool shock is sold in bags, bottles and also loose in buckets. Cal Hypo is not stabilized, so it won't add to cyanuric acid levels, but it will add a small amount of calcium to the pool. Granules dissolve quickly, but not instantly; pre-dissolve in a bucket of water when adding to vinyl liner pools.

  • Strength: 65% Pool Shock, 68% Granules, 73% Super Shock
  • Dosage: 1 lb. per 10000 Gals, adds 9-11 ppm depending on strength
  • Quantity: Sold in 1 lb. bags, bottles, or in 25 lb. and 50 lb. buckets
  • Rating: 4.8 Stars on 304 reviews
  • Cost: $2.60/lb to $3.60/lb

Sodium Hypochlorite

Bleach illustration, by istockphoto

Liquid chlorine can't ship by UPS/FedEx, but we can truck ship a case of 24 Gallons. Chemically identical to household bleach, pool liquid chlorine is typically a higher strength of 12.5%, compared to 5% concentration of regular bleach. Liquid chlorine is quick acting and leaves no residue, but has a very high pH of 13, and can be hazardous to transport and store. Pour directly into the pool for shocking, or use daily with a pool chemical pump to administer small doses all day long.

  • Strength: 5% Household or 12.5% Commercial Bleach
  • Dosage: 1 Gal. per 10,000, adds 7-14 ppm, depending on strength
  • Quantity: Sold in 1-Gal bottles, 5-Gal drums or delivered to 50-Gal vats
  • Rating: n/a
  • Cost:  $3-$6/Gallon, depending on strength and size

Sodium Dichlor

In The Swim Di-Zap Pool Shock shown

Dichlor pool shock such as our Di-Zap Multi-Shock, is a neutral pH, stabilized form of chlorine granules. Di-zap will last longer in bright sun, and contains no calcium for those with high hardness levels. Used monthly, there is no need for separate additions of cyanuric acid to the pool. Often used in saltwater pools or in pools with mineral or UV systems, or any pool that does not use stabilized chlorine tablets.

  • Strength: 56% Available Chlorine
  • Dosage: 1 lb. per 10000 Gals
  • Quantity: Sold in 1 lb bags and in buckets
  • Rating: 4.5 Stars on 14 reviews
  • Cost: $4-$6/lb

Potassium Monopersulfate

Chlorine Free Pool Shock from In The Swim

Non-chlorine shock, MPS has a fine granular texture that dissolves immediately, and won't affect pool pH levels. Leaves no residue or binders behind, and you can swim immediately. Chlorine free oxidizer has 4.5% of active oxygen, to destroy bacteria, chloramines, ammonia and clear cloudy water. MPS can be as effective as chlorine shock for any use, with exception to extreme algae or bacteria conditions.

  • Strength: 38% MPS
  • Dosage: 1 lb. per 10000 Gals
  • Quantity: Sold in 1 lb bags
  • Rating: 4.8 Stars on 111 reviews
  • Cost: $2.68/lb to $3.66/lb

Pool Perfect Plus Phos Free

Natural Chemistry Pool Perfect Plus PhosFree 3L shown

Not a shock treatment, but a unique way to reduce the need for pool shock treatments. Natural Chemistry has blended their most popular pool enzyme Pool Perfect plus PhosFree, to reduce chemical demand for any pool, eliminate algae and continuously clean your pool filter. Enzymes remove organics and oils from the water and filter, while the PhosFree removes phosphates that literally starves algae into submission. Regular use will reduce your need to use pool shock.

Other ways to reduce the need to shock a pool include maintaining impeccable water balance, a consistent and constant chlorine residual, and running the pool filter long enough each day to manage the continual inflow of particulate matter.

If you find that you need to shock every week, or the pool just isn't clear without regular shock treatment, you may look at your water balance, circulation or filtration - there may be performance issues there, requiring more pool shock as compensation.

In The Swim makes every effort to provide accurate recommendations based upon current ANSI/APSP/ICC-5 2011 (R2022) standards, but codes and regulations change, and In The Swim assumes no liability for any omissions or errors in this article or the outcome of any project. You must always exercise reasonable caution, carefully read the label on all products, follow all product directions, follow any current codes and regulations that may apply, and consult with a licensed professional if in doubt about any procedures. In The Swim assumes no legal responsibility for your reliance or interpretation of the data contained herein, and makes no representations or warranties of any kind concerning the quality, safety, or suitability of the information, whether express or implied, including, without limitation, any implied warranties of merchantability or fitness for a particular purpose.