Green algae is a common swimming pool problem, which may appear as a greenish growth on the floor and walls of a swimming pool, a green tint to the pool water, or greenish material suspended in the pool water. The only swimming pool chemical that will kill an algae growth is chlorine based swimming pool “shock”. Shock is a granular form of highly concentrated chlorine, which quickly raises the chlorine level of the swimming pool water. The elevated chlorine level makes the pool water conditions unlivable for anything organic, and algae quickly dies.
Before adding a dose of chlorine pool shock, the pool walls and floor should be brushed to remove as much of the algae as possible. This will greatly reduce the amount of time it takes to kill and clear the algae bloom. The normal “maintenance” dosage of most swimming pool shock is 1 lb. per 10,000 gallons. This dosage should be increased to 1 lb. per 7,500 gallons, or you should follow the manufacturer’s dosage suggestion for killing algae. Chlorine pool shock needs to be dissolved in a large bucket of water before it is added to the swimming pool. Always add chemicals to water when dissolving. NEVER add water to chemicals. The swimming pool cannot be used until the algae is dead, and the chlorine level of the pool water has returned to the safe range of 1-3 ppm.
The pool filter system should be running when the chlorine pool shock is added, and the filter system should continue to run 24 hours a day until all signs of algae have completely left the pool. Monitor your pool filter system closely and thoroughly backwash or clean the filter each time the pressure rises 10 psi. above the normal operating pressure. The dead algae that your pool filter collects may quickly dirty the filter, and need to be cleaned out frequently. If the conditions of the swimming pool does not significantly improve after 12-24 hours of filtering, add a second dose of chlorine pool shock at the increased rate. Once the algae is dead it will turn a white or grayish color, and it will be suspended in the pool water or settle to the floor. When there is no longer any sign of the color green in your pool, thoroughly vacuum the swimming pool. The pool filter should be backwashed or cleaned to be sure that dead algae is not trapped inside the filter. If the filter is not thoroughly cleaned the algae may quickly return.
Test and balance all of the pool chemical levels using the guidelines below, and pay particular attention to the chlorine level of your swimming pool water in the future. Algae and harmful bacteria are almost immediately destroyed by a chlorine level of 1 ppm or higher. You have experienced an algae problem because you have not properly maintained the chlorine level of your swimming pool, and it was allowed to drop below 1 ppm. Test pool water frequently and make any necessary adjustments for a clean, safe and easy to maintain swimming pool.
- Free Chlorine: 1-3 ppm
- pH: 7.2 – 7.6
- Alkalinity: 80 – 120 ppm
- Calcium Hardness: 200 – 350 ppm