Keep your pump and filter running. Give the shock a good 12 to 24 hours to work it's magic. If the algae hasn't cleared up after 24-48 hours, clean and brush the pool and add another shock treatment.
"Shocking" the pool with a large dose of chlorine is the most effective way to kill the existing algae and bring your pool back to sanitary conditions. This usually works within 1–3 days, but can take up to a week if pool conditions are poor.
You can get rid of algae quickly by vacuuming and brushing your pool, balancing your pool's water chemistry, and then shocking and filtering your pool water. Just be thorough as you clean your pool surfaces. If you leave behind even a small number of algae spores, it won't be long before they regrow and bloom again.
Chlorine is still one of the most effective killers of algae so doing a super-chlorination of 10-20 ppm of chlorine can go a long way towards wiping out the algae. Liquid chlorine is an ideal shock for algae because it is fast acting and does not add cyanuric acid (CYA) or calcium to the water.
While shocking and adding algaecide is effective in getting rid of algae, it should not be done together. This is because when you mix chlorine and algaecide together, it renders both of them useless. Hence, you should first shock the pool and wait for the chlorine levels to fall below 5 PPM.
Although, if you overdo the shock treatment, you risk getting green hair from chlorine due to the excess chlorine oxidizing the copper in the water. You can execute a shock treatment with a few different types of pool shock, just be mindful of how much you're using.
Pool algae can be caused by poor filtration, out-of-balance water, low or inconsistent chlorine levels, or poor water circulation. Green, dark green, yellowish green and blue-green algae are the most common. Green algae are slimy.
Shock Your Pool with Chlorine to Kill Algae
This is the main event in clearing a green pool—killing the algae. Pool shock contains a high level of chlorine that will kill the algae and sanitize the pool. For the best results, use a shock that contains at least 70% available chlorine (calcium hypochlorite).
A nylon or rubber brush is the correct choice for scrubbing the sides of a soft-sided above-ground pool. A large pool brush makes quick work of the job, but you may need a smaller brush to clean corners. Once the particles have been removed from the sides of the pool, turn your filter back on and agitate the water.
Grab a brush and some baking soda. Bicarbonate, the active ingredient in baking soda, is an effective spot treatment to help kill the algae and loosen it from the wall. Make sure you really get every last particle free; black algae has particularly long and stubborn roots which makes it a persistent strand.
If algae grow on the leaves and stems of your aquarium plants, create a routine of cleaning them regularly. Using a solution of 5-10% bleach, dip the plants for a few minutes as needed to destroy the algae. Make sure they are thoroughly rinsed because bleach can kill your fish. Invest in a filter.
A pool filter should be run for a minimum of 6 hours after shocking a swimming pool. This is to allow the filter to clean the water and give the shock enough time to fully mix with the pool water. Running the filter after shocking for 24 hours to 7 days is necessary if the pool has a large amount of algae.
The last thing you want to do is vacuum algae manually, which will contaminate your filter. Your pool will not clear up. In fact, the chances of your problem getting worse are very high. You'll also need to vacuum to waste when there is a large amount of debris or leaves in the pool, usually at opening.
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.
Now is the time to add Pool Clarifier and let it circulate for 12 hours. This will clump the algae together into vaccumable pieces. Shut your pump off and let the cloudiness settle. This may take up to a few days for very cloudy pools.
Pools can immediately turn green after shocking 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.
A good rule to remember is to use one bag of shock (1 gallon of liquid chlorine) per 10,000 gallons.
All you need to do is bypass the filter and pool vacuum for algae to the waste. However, this can only work if you have a multiport system or a waste line system in your cartridge filter. Vacuum the pool to waste after you have set up the waste, and the debris and algae will get out of your pool.
But is it safe to swim in a pool with algae? Whether mild or severe, it isn't recommended. Significant amounts of swimming pool algae welcome a breeding ground of harmful bacteria that feed on algae. These bacteria pose health risks to swimmers, most commonly resulting in a skin rash.
It's often recommended to shock your pool once a week. If you don't do it every week, you should at least do it every other week. This is necessary to maintain your pool's water chemistry. If you have a lot of people over in your pool or have a party, you may want to shock your pool more frequently.
It's pretty tough to over-shock your pool; shocking your pool two days in a row with the proper dosage for your pool volume shouldn't be a problem – and in fact, is sometimes even needed to rid your pool of algae and other contaminants.
We typically recommend using a calcium hypochlorite (cal hypo) shock when super chlorinating a pool. Just keep in mind that this type of pool shock has a small amount of calcium and will cloud the water for up to 12-24 hours in certain situations.
After Shocking Your Pool
It is safe to swim once your chlorine levels are around 5 ppm or after 24 hours. It is always best to test first!