Shock (Superchlorination)

So how do you handle a pool in which the combined chlorine level has become elevated? Unfortunately, just adding the usual dose of free chlorine to reach the usual ideal level of free chlorine won’t do the job. That would be like trying to push a lawn mower when the grass is already two feet tall. If your water testing confirms the presence of excessive chloramines (greater than 0.2 ppm), it is time to shock (superchlorinate) the water.

Shocking (SuperChlorinating) Your Pool

Usually a shock treatment requires a free chlorine compound in an extra large dose. You may need a dosage of three to six times the regular amount to remove these contaminants from the water. Higher levels of organic impurities may require even more chlorine.

As you add this higher dosage of free chlorine to the water, the measurable (total) chlorine level will rise until all the combined chlorine is oxidized. At that point, the total chlorine level will drop suddenly because the combined chlorine will disappear. We call that point at which all combined chlorine is completely oxidized the breakpoint.

To achieve the breakpoint, you generally have to add an amount of free chlorine that is 7 to 10 times the amount of the combined chlorine (chloramine) level. For example, let’s say that your water testing reveals that the pool has 3 ppm of combined chlorine. In that case, you may need 30 ppm of additional fresh chorine to oxidize or destroy all of the combined chlorine. Once you have reached the breakpoint in the water, you will notice a reduction of the odor and irritation caused by the chloramines. Only free chlorine will remain in the water after you have gotten to the breakpoint.

You can also oxidize the combined chlorine with Non-Chlorine shock (monopersulfate or Oxone®). Monopersulfate does not contain any chorine, so it will not increase the free chlorine level in the water. In fact, this product is not even a sanitizer, so you can only use it when you need to shock the water. (It will not leave behind any sanitizer residual to keep the water clean over time; it dissipates from the water right away.) One advantage of monopersulfate is that it does oxidize the water quickly. This will prove useful in many situations. When you shock the water with monopersulfate, the waiting time is very short before swimmers or bathers can reenter the water. (That is not true with chlorine shock treatments.)

When shocking a chlorine-treated pool or spa, you can use. . .