Technical Articles
Technical Bulletin: Don't Underestimate Nitrogen
Have you ever encountered a problem with your swimming pool water that makes you go crazy? Every parameter is properly balanced, yet algae plagues your pool. The water is crystal clear but you cannot maintain a free chlorine residual. These problems and others can be the result of a nitrate nitrogen build up in your water, and treating this problem may be a difficult task.
What is Nitrate Nitrogen?
Nitrate is a nitrogen compound that forms naturally in our soil and atmosphere. Nitrate compounds can also be present in water, which is why we may have to deal with them. Unfortunately, nitrate is like a rude in-law during the holidays. They cause problems and you want to get rid of them, but that won’t be easy to do. Nitrate, which consists of a single nitrogen atom connected to three oxygen atoms (NO3), is extremely stable. As a result, it can make its stay in your pool (or spa) waters an extended one.
How Do I Get It? (Not that I Want It)
Fertilizer is the most common source of nitrate intrusion. Many fertilizers contain a high level of nitrate nitrogen. Nitrogen can leach out of the soil; any nitrogen not used by the plants can be washed away by rain, a sprinkler or another water source. The nitrate can then wash into the pool or find its way into the water source that you use to fill the pool. This can be a serious problem if you live in an agricultural area, especially if you use well water in your pool. In addition, fertilizer overspray from nearby farms, gardens or lawns can increase nitrate levels. This is the main way that nitrogen gets into tap water. In fact, even city water may contain a low level of nitrates. The Environmental Protection Agency (the US government branch that monitors air and water quality) has set a maximum nitrate level of 10 parts per million (mg/L) in municipal water supplies. Therefore, the nitrate nitrogen may be at problematic levels from the beginning when you fill the pool with fresh water.
In addition to fertilizer, other sources of nitrate nitrogen are human wastes, rain, animal feces, and leaves or other decaying plantlife. Any one of these sources can introduce a significant amount of nitrates into the water. Normally this build up will occur over time as the source contributes nitrates again and again. A combination of these sources may build up even more quickly to have a negative impact on the water.
How Does Nitrate Affect the Water?
First and most important, nitrates will increase the sanitizer demand in the water. This means that they create a lot of extra work for the sanitizer to do, causing the sanitizer residual to become depleted more quickly. As a result, more sanitizer will be needed and more time and money will be spent on this pool. Even a small amount of nitrate, slightly above 10 ppm, will affect the sanitizer demand. Higher nitrate amounts will wreak havoc on the sanitizer level. A nitrate level at or above 50 ppm will cause the sanitizer demand to double, and the situation will become even worse as the nitrates build up further.
Second, the algae in your pool love nitrates like kids love ice cream. They will become uncontrollable in the presence of a high nitrate supply, making a mess before you know it. In fact, you are actually fertilizing the algae! Just as it feeds the plants that we grow in our gardens, nitrate helps algae to grow and develop into a beautiful green or some other color, although you may not appreciate the beauty.
If the nitrate level in your water is below 10 ppm, you should be able to control algae with regular methods. Above 10 ppm, you may need to add algaecide on a routine basis to prevent an algae bloom. Above 30 ppm, algae can start to get out of control. Ideal free chlorine levels may even be ineffective in preventing algae when nitrate levels are this high.
High nitrate levels have been known to baffle the most seasoned pool professional. Algae blooms can occur even when the water appears to be perfectly balanced. In a case like this, don’t forget to test the nitrate level! Otherwise you may waste hundreds of dollars trying to maintain an appropriate sanitizer level and destroy algae.
What’s the Treatment?
Prevention is the best method. First, determine by testing if the source water being used to fill the pool has a sufficiently low, ideally non-existent nitrate level. If not, an alternative source may need to be considered. Next, since you now know the other common sources of nitrate contamination, take steps to protect your pool from being invaded. Cover the pool when fertilizing, shower before entering the water, keep animals out, remove leaves from the water immediately, etc.
The only practical way to lower the nitrate level once it has exceeded the ideal minimum is to drain and refill the pool with water that contains no nitrates (or a very low amount). In most cases, you can accomplish this with a partial drain and refill. The nitrate level should not exceed 10 ppm.
Test the nitrate levels. Nitrate testing is really done as a trouble-shooting test. When you add fresh source water, test it to make certain that it doesn’t contain a high level of nitrates. In addition, you should test the nitrate concentration whenever there is an algae bloom. This may be a good indication that the nitrate nitrogen level is getting out of control (or already has). In addition, if nitrates have been a problem in the past, it is a good idea to test at least monthly to make sure it is not a reoccurring problem.
© 2001 Environmental Test Systems, Inc.
Joe Sweazy, Environmental Test Systems, Inc.
