1. Chlorine-containing products are the preferred algaecide. If the water in the pool is green or clearly contains algae clusters, there are not enough chlorinated products in the pool. Filling a pool with a large amount of chlorine-containing products is the most effective way to kill the algae buildup and restore pool hygiene. This usually takes 1-3 days, but can take up to a week if the pool conditions are poor. The other methods listed below, while faster, may not solve the underlying hygiene problem. It is also expensive and may have unexpected side effects.

2. Scrub the wall and bottom of the pool. Brush off as much algae as you can. This reduces the time it takes to kill and remove the algae. Pay special attention to the nooks and crannies where algae often gather behind steps and escalators. Make sure the brush fits the pool. Steel brushes are effective for concrete, while nylon brushes are suitable for vinyl pools.

3, check to determine the safety of chemical agents. Using this method can result in exposure to dangerous chemicals. So, be sure to read the safety information on the label first. At a minimum, follow the usual safety standards for pool chemicals: Wear gloves, goggles, and clothing that covers your skin. Wash your hands after use and check your clothes for chemicals.

Avoid inhaling chemicals. Be careful when dealing with chemicals in windy weather.

Always add the chemical to the water, not the water to the chemical. Do not return the wet spoon to the container.

Chemicals should be stored in sealed fireproof containers, away from children, on different shelves on the same floor (not one on top of the other). There are a lot of pool chemicals that explode when they come into contact with each other.

4, adjust the pool pH. Measure the pH of the pool water with a pool pH kit. If the pH is higher than 7.6 (which usually occurs when algae blooms), add a ph-lowering agent (such as sodium bisulfate) to the pool according to label instructions. The target pH is between 7.2 and 7.6, which makes chlorine more effective and reduces the growth of infection. Wait at least a few hours and then test the pool water again. Kits using tablets or droppers are much more accurate than test paper.

If the pH is back to normal but the total alkalinity is higher than 120 ppm, check the pH reducer label for instructions on bringing the total alkalinity down to 80-120.

5, choose a chlorine-containing product shock agent. Chlorine-containing products used for routine treatment of pools may not be the best choice for shock therapy. Ideally, a pool specific liquid chlorine product should be used. Liquid chlorine-containing products should contain sodium hypochlorite, calcium hypochlorite or lithium hypochlorite. If it is hard water, calcium hypochlorite should not be used.

Hypochlorite products are flammable and explosive. Lithium is safer but also more expensive.

Chlorine-containing products (such as dichloride or trichloride products) that contain stabilizers that must not be added to the pool in large quantities should not be used.

6. Add a large dose of shock agent. Check the "Shock" instructions on the label of the chlorine-containing product. To combat algae, twice the recommended dose of conventional shock therapy should be used. Triple the dose if the pool water is very cloudy, and quadruple the dose if you can't even see the top of the ladder. While the pool filter is running, add the shock agent directly to the pool along the sides of the pool. (For vinyl pool linings, pour the shock agent into a bucket of pool water first to avoid discoloration.) Warning - Liquid chlorine can explode and produce corrosive gases when exposed to chlorine-containing products in tablets or granules. Never pour liquid chlorine-containing products into pool skimmers or any items containing these substances.

Since UV rays in sunlight break down chlorine, shock therapy is most effective when added at night and left overnight.

7. Retest the pool the next day. After the pool filter runs for 12-24 hours, test the pool again. The killed algae turns white or gray and floats in the pool water or settles on the bottom of the pool. Whether or not the algae are killed, the pool water is tested again for new chlorine levels and pH levels. If chlorine levels are high (2-5 ppm) but algae is still present, these levels should be maintained for the next few days.

If chlorine levels rise but remain below 2ppm, a second shock therapy should be administered the next night.

If the chlorine content of the pool water does not change significantly, the cyanuric acid in the pool water may be excessive (more than 50 ppm). This is caused by the use of chlorine-containing products in granules or tablets, which can "lock" chlorine into an unusable form. The only solution is to administer shock therapy repeatedly (sometimes multiple times) or partially empty the pool.

A large number of fallen leaves or other substances in the pool can also eat up the chlorine in the pool water. If the pool is not used for a long time, it can take a full week and several shock treatments to correct it.

8. Scrub and test every day. Scrub vigorously to prevent new algae from growing on the walls of the pool. The chlorine should kill the algae in the next few days. Daily testing to confirm chlorine levels and pH levels are within acceptable ranges. The index values of a well-maintained pool are roughly as follows: free chlorine: 2-4ppm, pH: 7.2-7.6, alkalinity: 80-120ppm, calcium hardness: 200-400ppm. Small standard differences are common, so small deviations should not be a problem.

9. Suck up the killed algae. When there is no green in the pool water, use a vacuum cleaner to remove all killed algae until the water is clear. You can also skip this step and leave it to the filter, but only if you have a strong filter and are willing to wait a few days. If it is difficult to capture all the algae, coagulants or flocculants can be added to make them stick together. These preparations are all available at pool supply stores, but if it's a home pool, it may not be cost-effective to do so.

10. Clean the filter. If it is a deep water high efficiency filter, it can be set to backflush. If it is a cartridge filter, remove it, rinse the cartridge with a high-pressure hose, and rinse with diluted hydrochloric acid or liquid chlorine-containing products if necessary. If the filter is not thoroughly cleaned, the killed algae will clog the filter.