If your pool has turned green, it indicates growing algae and a problem with the chemistry in the water. A green pool should not be swum in. Before enjoying the pool, you need to remove all debris and green substance from the water and pool walls, as well as fix the chemical balance. Cleaning your water will take some time, so don't expect to be able to swim on the same day as you start your cleaning; chemicals themselves may take several hours to work before you can get in the pool.
Empty the skimmer filter, located along the side of the pool. Too much debris in the skimmer basket may prevent the filter from working properly.
Turn the pool filter on to help clean the pool water while you work on the remaining debris in the water. Pool filters only cleans floating particles in the water, not anything that is on the floor or stuck to the walls of the pool. Most pool filters should run at least six to eight hours a day, if not closer to 12 hours.
Remove floating debris, such as bugs and leaves, from the surface of the water with a net tool on a long pole. Dip the skimmer down into the pool to get any debris that may have gone to the bottom of the pool.
Turn the pump filter off and brush the sides of the pool with the special scrub brush at the end of the pool. Wait until all the debris has settled to the floor, and then turn the filter back on.
Engage the vacuum attachment to the filter and allow it to roam around the floor of your pool.
Clean the filter itself by turn the pump off and set it to the "backwash" setting. Allow the pump to run on backwash until the water runs clean, normally about one minute. Turn the filter to the "closed" setting and remove any debris trapped inside. Replace the basket and turn the filter on as normal.
Add water to the pool with hose, if needed, to get it back to the correct level.
Measure the width, length and average depth of your pool with a tape measure. This helps you determine how many gallons of water your pool holds and how many chemicals you need to add to your pool.
Take the pool measurements, and a sample of your water, to a pool supply store for professional help on how to keep your water clean and free from algae. Depending upon the current water quality, size of the pool and type of chemicals you use, the pool professionals will make recommendations for you on the type and quantities of chemicals to add. You'll likely need to add a "shock" chemical to the pool to kill any algae in the pool, and a pH adjuster to help balance the water and a chemical to clean the water, such as chlorine.
Retest the pool water with an at-home test kit, following the manufacturer's instructions on the package. Add more chemicals as necessary, and wait the recommended time on the product packaging before you swim in the water.
Check the water weekly to ensure you keep the water at the proper balance of water. Add more water to the pool as necessary to keep it at the proper balance.