What causes a high phosphate level in the pool? Our kit does not measure this but a pool store said this was important to check. (They found our level was 300 and we needed to lower it)

Question:

What causes a high phosphate level in the pool? Our kit does not measure this but a pool store said this was important to check. (They found our level was 300 and we needed to lower it)

Answer:

Phosphates can be introduced to your swimming pool from a number of different sources. Leaves, pollen, grass, etc. all contain some level of phosphates and can leach those phosphates into your pool if they are allowed to stay in there for some period of time. One way your grass gets its phosphates, from fertilizer, can be a source for your pool's phosphates. Overspray is common from grass treatments, perhaps even from neighbors or the golf course nearby. Animals also contribute a higher level of phosphates - ducks, geese or even the family dog. You and your family can contribute phosphates from the detergents in your clothes or other contaminants you introduce to the water. Last but not least, there are even certain pool chemicals that contain phosphates. Given all the sources, 300 parts per billion is only slightly higher than recommended.