Pool water consists of five basic chemicals. The five basic pool water chemicals are Alk, PH, Chlorine, Stabilizer and water hardness. Your pool water can become green if you do not have your chemicals within the proper range or your pool filter system could not be running / working the way that it should.
The first thing you will want to do is to check all of your pool chemicals and make sure that they are with the proper range that they are supposed to be. If any of your chemicals are low, you should bring them to the proper levels as soon as you can. For instance if you have no Chlorine in your pool water then its not your filter that is making the pool water green its actually the lack of Chlorine. So make sure your pool water chemistry is correct before you start to think there is something wrong with your filter system.
The second thing you will want to check is the pool filter to make sure its doing its job. You first will want to back wash your pool filter and if you have a DE filter you will also want to add more DE into the pool filter after you backwash the filter. If your pump is not working or after back washing the pool filter you still have bad water pressure into the pool, you then could have a problem with your swimming pool pump or filter. You will have to then troubleshoot the pump and filter to see what is wrong.
The fastest way to clear a green swimming pool is to make sure the water chemistry is balanced, make sure that the pool pump timer is set so the pool filter can run 24 hours a day, back wash your pool every 6 hours, and also triple shock your pool. If you take those steps you can have your completely green swimming pool 100% clear and blue in around 72 hours. Once you pool water is blue and clear again you will first want to check the water chemistry again and then add any chemicals that are needed. Run the filter for another 24 hours and then check the chemicals again. If all the pool chemical readings are within range you can go and set the timer for the pool pump to run 6 – 8 hours a day.