Shock is chlorine, in a high dose, meant to shock your pool and raise the chlorine level quickly. Chlorine tabs (placed in a chlorinator, floater, or skimmer basket) maintain a chlorine residual in the water. You do need to use both tabs and shock.
Simply add a chlorine neutralizer like sodium thiosulphate to quickly lower your free chlorine levels. A chlorine remover like this is a handy chemical for any swimming pool owner, especially if you have a tendency to overshoot and set your chlorine levels too high.
Heavy shocking with granular chlorine will generally require 24–48 hours before the chlorine level has dropped to safe swimming levels (below 5 ppm). Lithium and non-chlorine shock labels typically allow immediate swimming or a brief 15-minute waiting period, but check the package label to be sure.
Pool shocking is a process that involves adding chemicals — whether chlorine or non-chlorine — to the water in order to keep it balanced and raise the free chlorine levels. The purpose of shocking is to destroy any harmful bacteria, combined chlorine, or algae that could be lingering in your pool.
You should not add chlorine and shock at the same time, as it's largely redundant to do so. Ideally, you should shock your pool at night, so the sun cannot interfere and destroy the active chemicals before they can do their job.
"Shocking” refers to the process of adding chlorine or non-chlorine pool chemicals to the water in order to raise the "free chlorine” level. The goal is to raise this level to a point where contaminants such as algae, chloramines and bacteria are destroyed.
It's not too uncommon for your pool water to be slightly cloudy after shocking, especially if you use a granular chlorine shock. It typically takes about 24 hours for the granules to fully incorporate into the water and disappear. Most cloudy water issues after shocking should resolve within an hour or two.
Is it possible to shock your pool too much? Yes—excessive shocking of your pool will keep it at an elevated chlorine level. This will cause irritation of the skin and eyes as well as excessive wear and tear on your pool filter system, including excessive corrosion of all metal parts.
If you're dealing with an algae infestation, brush the pool after shocking to remove lingering debris and run the filter. Rinse or backwash your filter to avoid recontamination. If you've still got traces of algae, shock your pool again.
The effect of excess chlorine in pools is an alteration in pH levels of pool water, making it more acidic. Signs of high chlorine levels can include itchy sensations in the eyes, nose and throat, nausea, vomiting, dizziness, lung irritation, and skin rashes.
For example, some 1-pound bags of shock treatment can deliver 7 parts per million of free chlorine per 10,000 gallons of pool water.
Regardless of how frequently or what system you use to add chlorine to the water, the chlorine level should stay between 1.0 and 3.0 parts per million (ppm) to maintain a healthy pool.
In most cases, high chlorine levels occur when too much pool shock or too much chlorine is added to the pool—either due to a one-time mistake or from long-term buildup. Check for a dispenser malfunction, as this is another common way to over-chlorinate a pool.
Is it safe to swim in a pool with high chlorine? No, it is not safe to swim in a pool with high chlorine levels as it can cause skin and eye irritation, amongst other risks.
If you need to quickly lower chlorine levels in your hot tub, use a chlorine neutralizer, dilute the water with fresh water, or leave the cover off and run the jets to let the chlorine dissipate. These methods can help reduce chlorine levels to the recommended range of 1-3 ppm.
Chlorine will burn itself off naturally. Depending on how hot it is and how high your chlorine levels are will determine the amount of time needed. It could be quick or it could take a few days.
Vacuuming After Shocking
As mentioned, you should vacuum your swimming pool as much as possible to keep the job manageable. However, after shocking the pool, you shouldn't vacuum for at least 24 hours. Running the water pump during this period will allow the shock to do its job.
Low chlorine levels often cause green or hazy water, so if your water looks a little cloudy and you haven't shocked in a while, adding shock is the first step. It is always best to shock the pool in the evening, when the sun if off the water. If not, the sun will suck it out as fast as you add it.
While some mistakes are small and recoverable, adding pool shock through your skimmer will literally blow up your pool's filter system! The gasses created from the mixture of dichlor and chlorine chemicals in such a small chamber create a deadly explosion.
Calcium Hypochlorite: Also common known as “cal hypo,” this shock is the most powerful and fastest acting shock available. Both an oxidizer and sanitizer, cal hypo is quick dissolving and is the most frequently used in the pool industry. It will slightly raise your pH, so make sure you adjust pH while using it.
Algaecides act as a backup to your normal sanitization program and prevent algae from starting and growing in the pool. Algaecide should be added after every shock treatment.
Pools can immediately turn green after being shocked when they have metals like copper in the water. These metals oxidise when exposed to high levels of chlorine, which makes the pool water turn green. Adding a metal control product such as Zodiac Metal Remover will help to restore the pool water.
This is because the chlorine levels in the water can be very high, and can cause irritation to your skin, eyes, and respiratory system. It's generally recommended that you wait at least 8-24 hours after shocking your pool before swimming.