Nitrates are a nitrogen compound that forms naturally. Nitrates consist of a single nitrogen atom connected to three oxygen atoms and are very stable, which make it very difficult to deal with when it is in your swimming pool water. Nitrates enter the pool water in numerous ways. Fertilizers, decaying plant matter, rain, and even our tap water are among some of the sources of nitrates. The E.P.A. has set a maximum nitrate level of 10 ppm in city water supplies. Normally, nitrates will build up over time before starting to have a negative impact on your swimming pool water.
Nitrates will affect the pool water by increasing the sanitizer demand in the pool water, causing the sanitizer levels to deplete very quickly. The results can range from using more sanitizer than is normal for the pool, cloudy water that will not clear and will make the swimming pool more prone to algae blooms that either will not clear up or will start to improve but quickly turn green again.
Now for the answer to the biggest question, there is no easy way to remove the nitrates from your swimming pool water. The only way to remove nitrates is to drain and refill the swimming pool with water that is nitrate free. If you have a vinyl liner pool or a fiberglass swimming pool, you cannot drain the entire pool. With these swimming pools the pool owner will have to flush the water by removing small amounts of the pool water and refilling the pool until the nitrate level is reduced.