How Nitrates Occur

• What keeps the lawn green can cause havoc in the pool.Comstock/Comstock/Getty Images
  
  Nitrates can enter the pool from a number of different sources, all supplying high enough quantities to cause problems. Fertilizer is one of the most common sources for nitrates in the pool, whether that pool is in-ground or above-ground. Nitrates are among the major nutrients required for plant growth, and are contained in most fertilizers. An application of a dry fertilizer to the yard or neighboring property can raise the nitrate content of the pool. A tree that hangs over the pool can also be a culprit, not only because of the seeds and leaves it drops, but also because of the droppings of the birds that live and roost there. If swimmers jump in the pool before washing off makeup, lotions and perfumes, this can also add to the problem.
  
  

Early Signs

• High nitrate content can make the pool look like a stagnant pond.Hemera Technologies/AbleStock.com/Getty Images
  
  Among the earliest signs that the pool can be developing a nitrate problem are cloudy water and the rapid growth of algae. Algae in itself doesn't mean the nitrates are too high, as an improperly chlorinated pool can also be the cause of algae. But nitrates, as key nutrients that will aid in the reproduction and growth of plants, can cause blooms of algae to quickly appear on the sides and floor of the pool, even overnight. This algae growth, coupled with a recent fertilizer application by you or your neighbors, can be an indicator that the water should be tested for nitrates. If they're over 25 parts per million, that's too high.
  
  

Later Problems

• No one wants to swim in a Petri dish.Comstock/Comstock/Getty Images
  
  In addition to aiding in the development of algae, high nitrate content will also make it more difficult to get rid of the problem. Nitrates can interfere with the way the pool chemicals work, and can also bind with chlorine to make it ineffective. This will increase the amount of bacteria and microorganisms in the pool and lead to the development of problems that are invisible to the naked eye. If the nitrates in the pool are too high, chances are there is also a high amount of phosphates, along with pH levels that are constantly in flux as the chemicals try to manage the bacteria and algae.
  
  

How to Fix It

• Pools filled from wells will usually have problems with high nitrates.Jupiterimages/Polka Dot/Getty Images
  
  While there are no chemicals that can be added to the pool to get rid of nitrates, there are a few things you can do. Add some phosphate removers to bring down the phosphate levels that usually go along with high nitrates. Phosphates and nitrates act in similar ways to encourage algae growth and tie up chlorine, so lowering the phosphates will help manage any undesirable conditions in the pool. Shock and chlorine treatments can also help, and be sure that the pH levels are kept in an acceptable range -- between 7.2 and 7.6. If there are still problems with algae, partially draining the pool and refilling it can help clear up any issues. If you have well water, however, this won't necessarily help, as well water is usually high in nitrates.