Why you need pool shock

Because you have to... it's Step 2.

Shocking is as important as regular sanitizing with chlorine or bromine (step 1) and adding algaecide (step 3). All pools need to be shocked on a regular, weekly or biweekly basis. Period.

Shocking your pool weekly helps rid the pool of organic & inorganic wastes such as sweat, cosmetics, suntan lotions, body oils, urine, contaminants brought in by rain or wind or even fresh water that is added to top off or fill the pool.

Almost ALL common pool water clarity problems (including early algae growth, mold & slime) are due to the fact that pool owners don't shock the pool properly - especially at pool opening. Insufficient initial shocking sets the pool water up for "water clarity failure."

Proper shocking helps ensure that the sanitizer (chlorine or bromine) can concentrate on killing bacteria & algae rather than having to fight these other foreign materials. When a pool is properly shocked, the pool stays cleaner & actually sparkles, and is less prone to algae blooms and cloudy water. An added bonus is that you will use LESS chlorine over the course of the average swimming season.

Shocking should be done at least every week or 2 weeks from pool opening to pool closing depending on use & current conditions.  But there’s more to it! Are you shocking, trying to reach “break-point” chlorination or curing a chlorine demand? Let's explain the differences between the 3 needs and the various products used to do the job right. 

Let's get specific:

  • Regular shocking
  • Super Chlorination or Break Point Chlorination

If you have a "chlorine demand" situation, that's a whole different ball of wax and must be dealt with thoroughly and swiftly.


regular shocking

Just do it weekly or bi-weekly...

“Regular Shocking” is just that. The pool is otherwise clean & clear. Algae is under control. There is no haze to the water. When you test the water (done twice each week), the Total Chlorine level is equal to the Free Available Chlorine (FAC) level. There are no or minimal chloramines (chlorine combined with swimmer and organic waste - nitrogen) present. Pool shocking is Step 2 of Good Pool Care.

Regular pool shocking should be done once every 1 to 2 weeks from the time you open the pool until closing or winterizing. Regular shocking oxidizes (burns out or burns away) swimmer and organic wastes that accumulate in the pool water over time. Regular weekly or bi-weekly shocking also helps to prevent the build-up of chloramines.

These wastes include sweat, urine, lotions, cosmetics, “stuff” that is introduced from the wind & rain. More recently, there is a concern for “stuff” or wastes that are brought in from normal “top offs” of municipal (tap) water or well water.  

These wastes contribute to red, irritated eyes, hazy water, algae growth, and water that smells like it has “too much” chlorine. Actually there is not enough FAC. 

Red, uncomfortable eyes? That's not TOO MUCH chlorine, that's a build-up of chloramines because the there's TOO LITTLE Free Available Chlorine and too many combined chlorine molecules not doing their job.

Shocking helps to “re-chlorinate” the chlorine. A properly treated chlorine pool should smell fresh and be sparkling in appearance. Mono-persulfate shocks (MPS) are OK to use from time to time to oxidize wastes, but chlorine shocks such as Cal-hypo or lithium are the preferred product. Liquid shocks? Sorry, but they are just not strong enough. (11% versus about 50% available chlorine). Household bleach? Save it for the clothes in the laundry! Would you use pool chemicals to wash your clothes?

Typical doses (chlorine, bromine, salt, ionizer, Pristine Blue pools): BioGuard® Burn Out® 3 : (cal hypo) 1 bag per 10,000 gallons (or any part of) every week or 2 depending on weather and usage. Lithium): 1 lb bag per 6,000  gallons (or any part of) every week or 2 depending on weather and usage. NOTE: These typical doses assume that the water is CLEAR without any visible algae or other problems. DO NOT USE THESE PRODUCTS in biguanide treated pools; they are incompatible.

Red-eye from chlorine combined with nitrogen resulting in irritating chloramines. SHOCK THE POOL!
Red-eye from chlorine combined with nitrogen resulting in irritating chloramines. SHOCK THE POOL!

super shocking or break-point chlorination

“Break-point” or super-chlorination.

The need for “break-point” or super chlorination occurs when there is a build-up of chloramines or combined chlorine in the pool water. Pool shocking is an integral part of pool care with proper pool chemicals. Chloramines are a combination of chlorine and usually nitrogen. When the chloramine situation becomes “bad” it is because hydrogen has combined with the nitrogen to form ammonia. 

Chloramines can and do contribute to algae blooms and cloudy water. The more chloramines present, the more dull the water becomes. The pool doesn’t sparkle as it should. The added nitrogen becomes food for algae. The water smells like there’s too much chlorine, but the actual FAC (the chlorine that is killing bacteria) is low or maybe even zero!

Here’s an example: The total amount of chlorine in the pool is 2.0 ppm but the FAC is 1.0 ppm. That means there is 1.0 ppm of chloramines. Chloramines must be completely destroyed or they will produce MORE chloramines and the situation will worsen. 

When treating chloramines, it’s an “all or nothing” proposition. In cases of very high chloramines, it is often a good idea to use a monopersulfate shock (MPS) which will break up most if not all of these nitrogen bonds without adding more chlorine to the pool. This is good to do in cases where the FAC is over 1.0 ppm.

If your pool has less than 1.0 ppm FAC and lots of chloramines, follow that MPS shock with a solid chlorine shock of Cal-hypo or lithium shock. To reach break point, 10 times the amount of chloramines present must be reached to destroy the chloramines.

In the example above, you would need to reach 10 ppm of FAC to reach break-point!

Keep in mind that reaching Break-point chlorination, MAY NOT satisfy a chlorine DEMAND

Typical doses: Double or Triple the amount of regular shocking.