One of the common questions we get is whether our customers need to use shock to treat their pool or whether they can just put tablets in the skimmer.
What is Shock Treatment?
Chlorine is often the preferred choice for killing Algae and bacteria in a pool
Shock is generally a Chlorine based product, without a stabiliser. It is used to kill contaminates such as Algae or bacteria in the pool. Usually, it is granular or powered form.
When I test the chlorine in my pool what am I measuring?
Most basic test kits when you measure the chlorine level in your pool, you measuring the “Free Chlorine”, that is the Chlorine that is available to kill Algae, Bacteria and break down contaminants.
What I can I use to measure the Chlorine Levels?
There are several ways of measuring the chlorine levels in your pool.
The easiest to use, and often use for hot tubs are test strips. These often measure other elements as well as the chlorine, these other elements are often, alkalinity, pH and hardness.
A second option is a comparator, with these you take a pool sample and dissolve a tablet into the water and compare the colour. There are basic kits that will measure just the pH and free chlorine, while more expensive kits, can also measure other elements such as cyanuric acid and phosphates.
Chlorine Levels should ideally be between 2 to 3 parts per million.
How often should I shock?
Ideally you should shock once every couple of weeks, though at times of high temperature, rain fall or high use you may need to shock once a week. We recommend you measure the chlorine and pH levels and dose accordingly.
If you have a regular testing routine, for example checking the pool every couple of days, and are ensuring that you have appropriate dosing in place, you may find the need to shock the pool is a rarity rather than a regular occurrence.
What conditions might mean you need to shock the pool?
There are conditions where the pool may need to be shocked to bring up the chlorine levels.
These include
- High usage, as people we introduce contaminants in to the pool, such as sweat, skin cells, bacteria, lotions, urine etc. We also absorb some of the chlorine into our skins and where the cover is removed the sun can evaporate the chlorine.
- Periods where the cover has not been replaced. We recommend that pools have a cover in place when the pool is not in use. In the summer chlorine can evaporate from the pool, a good cover can reduce the chemical lose by up to 40%, it will also help eliminate water loss.
- When the pool water has been changed. When the water is changed there will be no chlorine in the pool water. Shocking the pool will add some chlorine to ensure that algae and bacteria cannot find a home to multiply.
- At end of the season when closing down for the winter. When closing your pool, it will often be shocked to a higher level than normal, the cold water over winter along with chlorine, will help keep slow algae and bacteria from growing during the winter months. We would also recommend checking and treating your pool halfway during the closed season.
- At the beginning of the season. Understandably it is impossible to stop algae and bacteria growth and there will be some algae in the pool when it comes to open the pool for the new season. At opening time, the pool will be shocked to help kill what algae is in the pool. If the pool was closed properly, treated during the winter and has a decent cover, it may not take may treatments to get the pool ready for use. However, If the pool has been left open, was not closed down properly, it can take a number of treatments to sanitise and clear the water ready for use
- After rain and storms. Rain water will dilute your pool water, when in the clouds it quite pure, but once it starts to fall it picks up contaminants from the atmosphere. Once it reaches the ground, it will pick up phosphates and other contaminants that will change the balance of your pool. This can create a condition where the chlorine is “used up” so shocking may be needed to raise the chlorine levels quickly.
In additional to the above, if you have trees and grass that are blown into the pool, be aware that these also contaminate the pool water.
Other considerations
Some people like to have chlorine tablets in their skimmer basket to slowly release chlorine into the pool, during high bather load or hot weather it is possible that these will not dissolve fast enough to keep chlorine levels to an adequate level.
During periods of warm weather, for our door pools, you will need to check your pool chemistry more often. Eighty percent of the chlorine in your pool can burn off in as little as two to three hours, especially if there is no cover installed.
If your pool starts turning green it is probable that the contaminants such as Algae and Bacteria are reproducing faster than the chlorine can act. In this case you may need to sharply increase the level of chlorine in the pool, sometime to ten parts per million. You should also check regularly (two days apart maximum) and re-shock. This is much the same process as opening the pool for the season.
Conclusion
As seen, there are many reasons that you may need to shock the pool. We recommend that you put in place a regular schedule for checking your pool, during warm weather check your pool chemistry more often and if you have a cover ensure that it is installed to minimise chemical and water loss.
Always read the instructions and dose appropriately.
As a final warning, always add chemicals to water, NOT water to chemicals, and avoid mixing different chemicals.
