I would say the number one contributing reason pools go green is neglect. Some other contributing factors are the use of wellpoint water, recycled backwash water and the purchasing of delivered water. Other factors include incorrect running times of the pump and dirty filters that are in need of a sand change. Incorrect water balancing will also affect how chlorine sanitizes your pool. High stabilizer (CYA) in your pool, higher than 100 ppm will require a higher chlorine level to sanitize your swimming pool water.

Not emptying baskets and leaf catchers will slow down filtration and the organics in the basket will consume chlorine, and before you know it, your pool is green. In order for the chlorine to be more effective in the killing of the algae that is clinging onto the walls for dear life, one needs to brush the walls and floor so that the algae drops into the water, and the chlorine can then do its job. When you have a high bather load, such as a pool party, or children playing in the pool daily, especially in summer, chlorine demand will be higher than normal. That is why it is important to super chlorinate (shock) your pool. Another reason for shocking your pool is to rid your pool of chloramines.