The following was published in a 6/18/90 industry magazine meant for pool and spa professionals. Although the article was written nearly a decade ago, not much has changed.
Nitrates is not a term most pool owners have heard. However ALL pool owners should be aware of their existence and potential for trouble. And while there isn't much we can do about most of the causes, we can control some of them.
Pool Emporium, Inc. does utilize a nitrates test, both for troubleshooting purposes, and as part of our routine in-store testing for every new customer.

Pool water or fertile stew?
By Eric Herman

Nitrate spread over crops, yards and anything else that grows is a life-giving compound: It is the primary component in most fertilizers and is essential to the development of all vegetation. Every time you see lush green, you are looking at nitrate's effects.
In a swimming pool, however, things that grow and turn green are unwelcormed and nitrate is the kiss of death. Nothing will engender blossoming algae and other waterborne plants in a pool or spa more effectively than nitrate.
Despite nitrate's critical role in the development of algae-related headaches, the pool and spa industry has yet to deal with nitrate as a specific issue. There are no seminars devoted to nitrate; there is virtually no literature on the subject; and many service technicians say they never consider nitrate when addressing a problem pool. Most significant, there are as yet no products on the market that are designed to remove nitrate from water.

Stable to a fault
Perhaps the main reason that nitrate is virtually ignored stems from the unfortunate fact that there is absolutely no way to oxidize it. Nitrate (NO3) consists of a single nitrogen atom attached to three oxygen atoms; it is extremely stable and will stay in solution very comfortably. Because nitrate is in a sense immune to oxidation, the only known way to remove it is through draining or dilution.
Service techs who are aware of nitfate's effects and have tested for it in problem pools will attest that it will turn even the best-kept pool or spa into a greenish mess.
"If you get nitrate in the water, you've got a problem," says George Warren, owner of George's Pool Service in Miami, Fla. "When you have a pool that keeps turning green no matter what you do it's probably nitrate."
Nitrate is found in the air, on the ground and in groundwater. It occurs in nature as animal waste and through the ionization of oxygen and nitrogen atoms in the atmosphere during thunderstorms.
The main source, however, is man, mostly through use of fertilizer in agricultural operations as well as through septic tank leaching. Because of its direct relationship to animals and farms, nitrate contamination of groundwater is particularly pronounced in rural areas.
Another nitrogen compound, nitrite (NO2), is also found throughout nature and, like nitrate, is an effective form of plant food. When introduced into a chlorinated environment such as a pool or spa, however, nitrite quickly gains a third oxygen atom and becomes nitrate.

Tracking the problem
Despite nitrate's relative obscurity in the pool and spa lexicon, there are a few people in this industry who have studied it. The man generally credited with first examining the relationship between nitrate and pool water is industry veteran John Girvan, president of the John Girvan Co., a manufacturer of pool chemicals in Jacksonville, Fla.
In 1965, Girvan set out to learn why some pools that were otherwise in perfect condition were turning green and using inordinate amounts of chlorine. After examining water from literally thousands of pools in his laboratory, Girvan discovered that nearly all of them had one thing in common the presence of nitrate.
"We wanted to find what it was that we couldn't see, taste or smell that was turning these pools green," he says. "Through a process of elimination we found nitrate. Nitrate will feed algae faster than any legal sanitizing system can kill it.
"With nitrate in the pool," he says, "you will get algae and other contaminants that won't respond to normal treatment."
Through the years of field and lab work that followed Girvan's initial findings, he discovered that nitrate finds its way into pool water by five basic avenues:
Fertilizer - far and away the mostcommon nitrate source. "We have actually had tests run where a pool that showed a zero-parts-per-million nitrate level the day before fertilizer was added to a nearby lawn or garden will pick up 10 to 30 ppm nitrate after a single dusting of dry fertilizer," Girvan explains.
Because nitrate will drive sanitizer consumption through the roof (see the chart) and the only way to remove it is by draining; asking gardeners and landscape contractors to be careful when fertilizing can be a cost-saving move.
Birds - the second leading nitrate source. According to Girvan, Florida's screened pools ironically are at greatest risk because of birds' preference for sitting atop the permeable structures. With even a modest flock perched above the pool, a substantial quantity of nitrate-rich feces can be easily dispensed onto the screen; when rain rinses the material into the pool, nitrate levels can jump to between 10 and 20 ppm.
Large, overhanging trees at pool-side can also contribute to the same bird-generated greening affect. "Some people put up fake owls to scare away the birds," Girvan says.
Human wastes. Urine and particles of feces can add double-digit nitrate levels depending on the bather load and how careful those bathers are about tending to nature's call before they enter the pool.
Spas are particularly susceptible to the effect of bather load because of the added problem of sweat and body oils. Problems stemming from nitrate contamination is one more reason to be sure to drain spas on regular basis.
Thunderstorms. Because lighting ionizes nitrogen and oxygen in the air, subsequent rain can actually boost the nitrate levels as much as 5 to 10 ppm.
This isn't the most common source of nitrate contamination, but Girvan notes that it's enough to create green water in what should be a healthy, nitrate-free pool.
Tap water. This is the least likely but most troubling means of introducing nitrates into the pool. When this happens, you've got a real problem because draining and refilling will only add more nitrates.
More important however, when nitrates are in the household's water supply, it means that people are drinking it and that represents a serious public health problem.

Testing the waters
Even though your only remedy for nitrate in the pool is either dilution through partial replacement or elimination through complete draining of the water, knowing that the contaminant is actually there is the first step in the battle.
Tests for nitrate are available, but they are relatively difficult to use and they take time. Tom Metzbower, director of sales and marketing with Taylor Technologies, a manufacturer of water-testing kits based in Sparks, Md., notes that using his company's nitrate test is not likely to become part of the service technician's routine.
"If at all," he says, "you are going to use this on a troubleshooting call. If you are someone who is on a service route, obviously you are concerned with time so this is not going to be part of your regular service, even with the zinc reduction test that we've developed, it takes a few minutes to develop a color for comparison."
Whether or not a removal system for nitrate will ever be available to the pool and spa service industry and to the rest of the world for that matter remains to be seen.
In the meantime, technicians should be aware that fertilizer, birds and careless bathers can add nitrate to the water. If you have a problem you can't pinpoint using your usual diagnostic skills and equipment, it maybe be time to test the water for nitrate content. If the results come back positive, be prepared for an uphill battle.

Nasty numbers
The presence of nitrate in pool water will drastically increase your sanitizer consumption - but just how much? The following chart is based on data provided by John Girvan, president of The John Girvan Company in Jacksonville, Fla. The levels are approximations only and serve solely to illustrate the potential effects of nitrate.

Nitrate Concentration (ppm)

Added Sanitizer Consumption %












"out of control"

* Girvan notes that between 30 and 50 ppm, algae can be controlled with the use of an algaecide and additional sanitizer. This, however, is not recommended. Instead, he prefers either partial or total replacement of the water.

This article was provided courtesy of POOL & SPA NEWS®