Pool Shock Treatments - Which One Not to Use!

by Pool Builders on 03-01-2010 in Articles

Swimming pool shock treatments are applied frequently to oxidize or "burn-up" excess chloramines, waste products and contaminants that accumulate in the pool water. Shocking the water is necessary, no matter which type of primary pool sanitizer is being used. The primary sanitizer becomes overburdened by the contaminant build-up. If the pool water looks dull or cloudy, most often this means the pool requires a shock treatment, but this is not always the case. Improper filtration or other chemical imbalance can also cause cloudy water. We also recommend occasionally using a chlorine-free pool shock such as monopersulfate, which is an oxygen-based shock, to remove all the chloramines. Some of the chloramines, including the organic type are not always destroyed completely by chlorine treatment. We recommend shocking your pool about once weekly, and more often after periods of rain, increased bather loads, and during long hot spells.

What type of shock treatment should you use? There are five types of shock or oxidizing agents used to chlorinated pools and spas. The type of pool shock that you choose to use is determined by how you choose to apply it into the water and will it case harm to the interior pool finish, such as concrete, fiberglass, vinyl liner, etc.

Potassium Monopersulfate (Oxygen based treatments) are non-chlorine oxidizers. Oxygen shock treatment is very good at removing excess contaminants and restoring the fighting power of chlorine sanitizers. Oxygen shock is also commonly called "safety shock" because pool bathers may safely return into the water about 15 minutes after treatment. There are no side effects on the pool water.

Sodium Di-Chlor [Di Chlor] is a granular form of stabilized chlorine that is 100% soluble. Di-Chlor may be used on all pool finishes without harm. It does not upset the pH balance of the water, cause foaming or require pre-dissolving. Because Di-chlor contains chlorine stabilizer (Cyanuric Acid) it will cause the stabilizer to build-up to an unsafe level. The pool will then have to be drained and refilled with fresh water when this occurs.

Lithium shock has the same properties as Di-chlor with one exception, it is not stabilized and therefore will not cause a high cyanuric acid level.

Sodium Hypochlorite is liquid and a strong bleach concentration. It is fast acting after addition to the water. It has an approximate 90-day shelf-life.

Calcium Hypochlorite [Cal-Hypo] is the most widely used and the strongest form of chlorine shock treatment. It is available in concentrations of: 47%, 65%, 68%, 73% or 78% available chlorine. This type may be used on all pool finishes, but it must be pre-dissolved before adding it into the water or it may bleach the color from a vinyl liner pool. It contains calcium that may cause temporary foaming or clouding. Cal-Hypo 47% available chlorine is a low-grade shock being sold primarily in many mass merchant stores. This product in our opinion should not be able to be labeled "Pool Shock". We consider the recommended dosage is too weak to achieve a true chlorine shock level of 5 to 10ppm in the water. It will require more of this product achieve the desired result. These blended products use special formula combinations and are being sold using various trade names. They all contain some chlorine blended with other chemicals like clarifiers. The sale of this product is not limited to just mass merchant stores.

The chemical manufacturers and suppliers embrace this blended product so strongly, that some have decided to discontinue stronger forms completely. Their reasoning has some merit. This is a safer class of oxidizer, so that increases handling safety, which in turn requires less governmental regulation, and increases their profits by helping to reduce many facets of the manufacturers overhead and transportation costs. That is all well and good, but pound for pound, the consumer will still have to pay a lot more to achieve the same result. We discourage the use of this type of product; not because it's a bad product, but only that it costs so much to effectively treat your pool. In many cases it costs the same or more than a full strength chlorine treatments! You have a choice to spend money more wisely.

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