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Dealing with nitrates

If algae problems occur, pool professionals need to test for high nitrate levels, which can present a number of water quality problems.

By Joe Sweazy

When a customer brings in a water sample complaining about an algae problem, pool and spa professionals must ask themselves which chemical parameters to include in the subsequent test. If their answer does not include testing for nitrate nitrogen, they could be ignoring a key factor. In fact, nitrate nitrogen testing should be considered in every situation with a potential algae problem.

High nitrate levels can present a number of water quality problems; before these can be fully addressed, one must understand what nitrates are, how they get into the water and impact water quality, and what to do to control them.

What are nitrates?

Nitrate is a nitrogen compound that forms naturally in the soil and atmosphere. These compounds can also be present in swimming pool (or occasionally spa) water, although many times pool and spa professionals are not aware of their presence. Nonetheless, they are all but inevitable and must be addressed.

A nitrate comprises a single nitrogen atom connected to three oxygen atoms (NO3). Nitrates form under the right conditions when nitrogen is introduced into the water. Typically, the nitrogen first forms nitrite (NO2), which quickly steals another oxygen atom from somewhere else to form nitrates. These additional oxygen atoms often come from hypochlorous acid (HOCl), the ‘killing’ form of chlorine, which leads to an increase in overall chlorine demand. Nitrates are also extremely stable, making it easier for them to stay alive in the pool environment.

Where do nitrates come from?

If the family dog swims in the pool regularly, nitrate levels can grow significantly.

Nitrates are often present right from the water source. As a result, nitrate problems have the potential to start as soon as the pool is filled. The U.S. Environmental Protection Agency (EPA) has established National Primary Drinking Water Regulations (NPDWRs) that allow nitrate nitrogen levels to be as high as 10 parts per million (ppm) and nitrites as high as 1 ppm in municipal drinking water. Fortunately, these nitrate nitrogen levels are not enough to cause significant problems; however, when combined with other sources of nitrogen, problems are likely to occur.

Fertilizer is one of the more common nitrogen sources; even small amounts can make a large difference in the pool environment. While nitrogen is a key nutrient that keeps lawns and plants plush and green, it is not ideal for swimming pools. This issue is of particular importance for homes adjacent to golf courses or other vast green spaces. Consider the amount of fertilizer required for turf upkeep; there is a high likelihood it will make it into nearby backyard pools. This also holds true for neighbours who use a professional lawn service. On a windy day, sprayed fertilizer can drift right into neighbouring backyards.

Other sources of nitrate nitrogen include human and animal waste, rain and leaves or other decaying plant life. If, for example, a dog or resident ducks regularly swim in the pool, or material from a nearby tree tends to drop in the water, nitrate levels can grow significantly.

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