nitrate/nitrates pool water problems: water chemistry - dealing with pool water nitrate/nitrates problems

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Nitrates can promote the problem growth of algae in swimming pool water and can enter the water from such sources as: decaying plant matter, fertilizers, contaminated well water, acid rain, contamination with soil, ground water runoff, bird droppings, bather wastes, urine and sweat. Nitrate is a vital plant nutrient and the presence in swimming pool water, above 10-25 PPM, can cause accelerated algae growth in poorly maintained pools. Pools, that are properly maintained, usually do not have unexpected difficulty controlling algae, even in the presence of low levels of nitrates. Higher levels of nitrates can make algae control more difficult and increase the amount of chlorine required to maintain satisfactory control of algae It is possible to remove nitrates by placing packets of ion-exchange resins in the skimmers, but the most practical and common method is water replacement. This is practical only if the new water is virtually nitrate free. Testing for nitrate is not common, but in those cases where algae control is proving difficult, despite apparently ideal pool water conditions, testing for nitrate and phosphate might be advantageous. Clicking on the underlined and highlighted "keywords" or "catch phrases," in the archived answers will give you access to additional information on that topic or product. Please refer to the Glossary, if there are terms or phrases that require explanation.

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More information about Nitrate Test Kits can be found by clicking on the above image. Helps you control and minimize its possible effects on recurring algae problems. Be better informed and avoid costly problems!

► Nitrates In Pool Water?

I've had some algae problems and have been told that it is due to nitrates in my pool water. Is that possible and what can I do about it? Thanks a lot.

Gloria B., 4/22/2003

Nitrates can certainly be a problem, especially above 10-25 PPM. They are a vital algae nutrient and literally act as fertilizer. If the nitrate level is low, you should be able to control the algae using standard shock, chlorine and algaecides. The use of a phosphate eliminator might be a good idea: it will help deprive algae of vital phosphate nutrients. Nitrates can come from a variety of sources: agriculturally contaminated well water, fertilizer, surface runoff contamination, sweat, urine, decaying plant matter, acid rain and wind blown debris. Trying to determine the source might help in controlling the problem. It is possible to lower nitrate level with the use of iron-exchange resins, but is not really practical. The replacement, of all or part of the water, is the most common method to reduce nitrates. I hope that I have been helpful.

Sincerely. Alan Schuster, 4/22/2003

► Mistaken Notion?

Hi Alan! Thanks for taking the time to setup this website. I've found it very informative and answers a lot of the questions that I have as a pool owner.

A couple of questions:

1-The pool store where I take samples of my water have indicated that the reason I'm having problems with algae is the nitrate content in the water. I've tested it and it looks like it is in the 10 PPM range which based on the FAQ is within the acceptable range. Now the question, I have an 80,000 litre pool and they have indicated that I must put in 50 - 80 litres of liquid chlorine (shock) to get rid of the nitrate. Is this accurate? Should I be concerned about the nitrate level?

2-Everybody seems to have a different answer to backwashing my sand filter. I usually backwash it when the pressure noticeably creeps higher than normal. I usually turn the filter on waste for 30 seconds, backwash for 2 minutes and then rinse for 30 seconds. Is this the correct backwashing procedure? Thanks.

Rick G., 9/18/2003

It is true that nitrates can add to the possibility of algae problems, but it is not inevitable. A 10 PPM level is not excessively high and should not be causing inevitable problems. The only way to lower the level would be to replace water and what is the nitrate level of the new water? Adding chlorine - no matter how much - will not lower the nitrates level one bit! Adding that amount of chlorine will have an effect on the algae, as well as your wallet. It is mistaken to think that chlorine, at any level will reduce nitrates. If you are having algae problems, pay more attention to the Free Chlorine level, pH and try using algaecide and/or a phosphate eliminator. A level above 25 PPM is considered too high and should be lowered by water replacement. A somewhat dirty sand filter is more efficient that a sparkling clean filter. Backwash when the pressure rises too high and/or the water flow is too low. Backwashing unnecessarily or too often will reduce the effectiveness of the filter. To improve the efficiency of your sand filter you might consider replacing the sand, with Zeobrite sand replacement filter media, the next time the sand need replacement. I hope that I have been helpful.

Sincerely. Alan Schuster, 9/18/2003

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► Low Chlorine Readings?

I was just wondering if the free chlorine level would be low (.2) and the total chlorine level high (3.0) because we have traces of nitrates(12ppm) in our well water? We started the season with good chlorine levels, but after we topped off the pool (and then it rained a LOT) the free chlorine level is very low. The local pool store said to "triple shock" the pool, wait 3 hours, measure the free chlorine level and continue this process until we show free chlorine for 24 hours. We have already dumped 30 bags of shock into the pool and the free chlorine level is still non-existent! Please help! Thanks so much!

Kiki, 6/27/2003

Nitrates do not consume chlorine. A concentration of 12 PPM is manageable and should not present unusual problems. High is considered over 25 PPM. What nitrates do is stimulate algae growth by providing a necessary nutrient. In the presence of adequate Free Chlorine levels, the algae should be under control, even with low levels of nitrates. You have to add enough chlorine to boost the Free Chlorine level into the optimum range of 1-3 PPM. While you have added a considerable amount, the non-existent readings point to the fact that not enough has been added. Make sure that the chlorine test materials are working properly, by having another source confirm the readings. For free chlorine testing, I suggest using LaMotte Insta-Test strips, as they provide the right kind of information. Go to: www.lamotte.com To better assure proper overall pool water chemistry, visit a pool store that has a very reliable, professional lab such as a WaterLink or Pinpoint system, rather than a less accurate test kit or strip reader. To locate a dealer near you, go to: www.lamotte.com/pages/pool/expdeal/index.html I hope that I have been helpful.

Sincerely. Alan Schuster, 6/27/2003

► Hot Tub Chemicals?

I have a new hot tub, 1325 litres. The company recommends a treatment program consisting of several chemicals. This series of chemicals is used to treat hot tub water and starts with a product which is a granular chlorine. After addition, the water is let be for 12 hrs before adding any other product. Assuming pH, alkalinity, etc. are OK, then you add a product which is an Oxidizer and a Clarifier. This procedure is supposed to last approx. one week, with only having to keep the chlorine @ 3+ ppm. The pH and alkalinity have to be maintained. My question is, having gone thru a case of "folliculitis", is my tub receiving the proper sanitation with this system and , if not, can you recommend a proper type and procedure? I should mention also that every time I use the tub I get itchy where the "folliculitis" was. Please help.

Ken M., Chatham, Ontario, Canada, 1/14/2004

One of the consequences of failing to maintain a proper 1-3 PPM level of Free Chlorine is the possibility of folliculitis. The only chemical that you are adding, that is a sanitizer, is the chlorine product. I suggest that you test for Free Chlorine, before and after each use. If too low, add more chlorine and allow 1/2 hour to sanitize before retesting and using the spa. It is a good practice to shock the spa at least once a week, after periods of heavy usage and at distinct signs of a loss of water quality. This will help to rid the water of organic buildups and prevent the development of resistant microorganisms. It is a good practice to shock the spa at least once a week, after periods of heavy usage and at distinct signs of a loss of water quality. This will help to rid the water of organic buildups and prevent the development of resistant microorganisms. Please refer to the archives for more information on chlorine alternatives and related topics. I hope that I have been helpful.

Sincerely. Alan Schuster, 1/14/2004

► Nitrates - Phosphates Relationship?

I have a pool that is having problems with nitrates. My free chlorine level is 0.5 and I was told to add a phosphate eliminator to help reduce the nitrate level. I added 1 cup for the past 2 weeks and it hasn't made a dent in the nitrates and I shock my pool every week. Please help, any suggestions will be greatly appreciated. Thank you.

Tom, 5/302005

Someone is just a bit off the mark! Phosphate eliminators will not reduce the nitrate levels, just the phosphate levels. What you should have been told is that there is no practical way to eliminate the nitrates. Nitrates and phosphates are both vital plant (algae) nutrients. Being that you can't remove the nitrates, it becomes even more important to remove the phosphates. You're doing the right thing for the wrong reason. Have the water tested for phosphates and see how you're doing. I hope that this information proves helpful.

Sincerely. Alan Schuster, 5/31/2005

► Is It Toxic?

The level of nitrates in our pool is 25. Is that considered toxic? Do we have to drain our pool?

Chris D., 6/17/2003

At 25 PPM you at the limit. It is not a matter of toxicity. Nitrates can promote algae growth. Higher levels could lead to a constant battle. You can't keep nitrates from getting into the pool water from multiple sources. I would not do anything. If you reach a point that you are encountering difficulty controlling algae, I would replace part of the water in the pool. In the meantime, keep a good chlorine level, maintain the water chemistry and pool water clarity. Enjoy the summer.

Sincerely. Alan Schuster, 6/1/2003

► Dealing With High Nitrates?

Your site is very informative and I have passed the link along to my friends. I have a 40 x 23' plaster pool. I had the water tested and they are telling me that I am off the charts on my reading for nitrates. I thought I heard a guy say over 80 but not sure. All I know is the the test they did should have taken 5 minutes and mine was already way up at about 30 seconds. They are telling me to replace the water in the pool. Here is my question. If the algae are feeding on the nitrates shouldn't they be decreasing the nitrates in my pool? Should I let my pool go for a couple of days to allow the algae to dine on the nitrates and then do a partial replacement of the water in my pool? I have 24,000 gallons so I could take out and replace 18,000 gallons and then treat whatever algae is left with algaecide and shock. Does that make sense or am I way off the mark? I keep thinking about other replies you had on your site about how the algae like to dine on the nitrates and phosphates, so if I let them eat the nitrates and remove the phosphates shouldn't they eat themselves out of food and die on their own? I think I am simplifying this too much but that seems like it should work? Not sure how quickly they eat the nitrates though? I really don't want to pull the pressure plugs is what it comes down to so can I get away with a partial water change (3/4 of the water)? And would that 3/4 water change be enough to bring down the nitrates so that I can get my pool back to relative normalcy? Thanks for your time

Bob R., 5/19/2008

Interesting question! If you allow algae to grow and pump out algae and water, you will remove some of the phosphates and nitrates. If you use chlorine to destroy the algae, these minerals will merely be recycled. I am not sure how much the nitrates can be lowered by this desperate measure. A nitrate test should take 5 minutes minimum. If they did it sooner, the true answer could be higher. Ask for the actual number. This time mix one part of pool water with 9 parts of distilled water. Multiply their test result by 10, to get the true reading. I would also have the tap water tested. If you are going to replace any of the water, you need to know if the new water is actually going to make a difference. The nitrates just didn't happen overnight. While it is impractical to remove nitrates, if you remove the phosphates, you will diminish the effects of the nitrates. That is what I suggest you do. Get the phosphates down to 100 PPB, by adding a phosphate eliminator, maintain the free chlorine at 2-4 PPM and keep the pH closer to 7.2. I hope that this information proves helpful.

Sincerely. Alan Schuster, 5/19/2008

► Low Nitrate Level?

I have a 38,000 gallon pool. The nitrate reading is 10ppm. I have been struggling to maintain a chlorine reading this season and recently started getting a bit of algae. The water looks amazing and the algae clears up with a touch of a 3" dichlor tablet. I am however dumping more chlorine and shock into the pool then ever before. My pool company suggests a partial drain and refill...do you agree? As it is the beginning of summer and my chorine demand has been low I am worried the problems will only get worse as we use the pool more and the temps rise. Thanks.

Linda H., 6/12/2006

Nitrates can be a problem. However, the concentration of nitrates has to be considered. Levels under 10 PPM are manageable. 10-25 bear some consideration of treatment. Over 25 PPM is a problem. Before doing anything, you should have the pool and replacement water tested. If present, there is no practical means to remove, other than water replacement. In place of removing nitrates, you should remove the phosphates, as this will deny the algae another vital nutrient and mitigate the presence of nitrates. If you opt to remove water, discuss this with the pool dealer or builder. Do it quickly and don't drag it out! I hope that this information will prove to be useful.

Sincerely. Alan Schuster, 6/12/2006

► Dealing With High Nitrates?

I have a built in pool, 22,000 gallons. I opened it this spring, cleaned and shocked it. It tested high for combined chlorine, so I was told to shock again, 15 lbs. shock. Tested again, told to shock again, 20 lbs. of shock, also told at this point nitrates were at 52 ppm. We had a lot of rain, about 5" added to our pool. Took in another water sample, a different person did the testing this time, and said nitrates were at 47 (I guess the rain diluted them a bit) and not to bother putting any more shock in, that the pool needs to be drained. I was also told they cannot get accurate chlorine test readings when the nitrates are this high. This will be a huge expense, since he said our 9 year old liner will not survive the draining, and will also have to be replaced. I guess this is our only option? I had our well water tested at the pool store also, and it was high in nitrates, at 20 ppm. I am now waiting on a second test on our well water from another lab, and recommendations on that. My questions are: Are there any other options for us, besides draining the pool? And, while we are waiting to have this work done, is the water unsafe for my teenage kids to swim in? The pool looks beautifully clean and clear, it's hard to tell kids they can't go in it when it's 90 degrees outside! Help! Thanks.

Kathy R., 6/6/2006

It is not the end of the world and it is not a matter of safety. The presence of high nitrates (over 25 PPM) makes algae control a bit less forgiving. If you allow the free chlorine level to bottom out, it will grow sooner and faster. Therefore, keep better control of the free chlorine level and you should be OK. You can't remove nitrates, but you can dilute them down. Consider replacing 20% of the water every week for a few weeks. That will slowly drop the level. While you can't remove nitrates, you can eliminate phosphates. This is another vital algae nutrient and removing it is the next best thing to removing nitrates. Deprived of phosphates, algae growth will be impeded. If the water is clear, there is no slime on the walls and the free chlorine is good, there is no reason not to enjoy the pool. Just monitor the free chlorine carefully. I suggest using a test strip such as the LaMotte Insta-Test, as it provides the right kind of information. I hope that I have been helpful.

Sincerely. Alan Schuster, 6/7/2006

► Nitrates?

Are nitrates a factor in pool water? Should I test my customer's water for it? Thanks for the help.

John T., 4/23/2003

Maybe! Just finding a low level of nitrates does not necessarily indicate a problem. You can't keep emptying pools because of its presence. However, when a pool is experiencing great difficulty controlling algae, even when all reasonable steps have been taken to control the algae, it might be a good idea to test for nitrates. This is especially true if there is a known source for the nitrate contamination such as agriculturally contaminated water. Levels above 25 PPM are considered potentially problematic and can result in increased chlorine consumption. To lower the nitrate level, water must be replaced. I hope that I have been helpful.

Sincerely. Alan Schuster, 4/23/2003

► Green Won't Leave?

My pool water tests perfect, time and time again. But still I am seeing periods of green water, even though I am adding lots of chlorine. The dealer has mentioned nitrates as a possible cause. Is this a possibility? Thanks for the reply.

Fred C., 8/11/2004

Nitrates are a distinct possibility. They act as fertilizer for the algae and can increase chlorine consumption. If the pool water shows a nitrate concentration of more that 25 PPM, replacement of water might be a good idea. Knowing the probable source of the nitrates is important, in order to help avoid or minimize a recurrence. There is no chemical means of nitrate removal. I hope that I have been helpful. Good luck.

Sincerely. Alan Schuster, 8/11/2004

► Partial Refill Is Not Best Option?

We tried an open our pool a little early and have had a stormy spring. The result was I have just removed a ton of leaves in the attempt to reopen. I adjusted the alkalinity and pH to proper levels and used a polymer algaecide, along with 6 lbs of rapid shock just three days ago. The pool has turned from green to a cloudy blue. I have some remaining green on the walls. I tested the water today, and everything is right except for a 0 free chlorine reading and a minimal total chlorine reading. When the dealer tested the nitrates he said I was at 4.5 ppm and that I was wasting my money by adding any more chlorine or shock and that I would need to begin a series of waste water removal below the skimmer and refills that could take up to nine or ten cycles. I have begun this cycle this evening. Is this correct? I have a vinyl liner pool no bottom drain 30000 gallons

Mike C., 5/24/2006

Levels under 10 PPM are considered manageable with proper chlorine levels. You might want to have the phosphate level tested. That you can do something about. Eliminating phosphates make nitrates less of a problem, because this other vital nutrient has been moved. I would not drain the water. It you follow his recommendation, you will never get it to zero. Probably not even below 2 PPM, even after 8-10 replacement of 10% each. I would work on getting a stable free chlorine level. You want some free chlorine to last through the night. Once done, there should be improvement in the water quality. By maintaining a consistent 1-3 PPM level of free chlorine, the nitrates should not present an insurmountable problem. For testing, I suggest the LaMotte Insta-Test strips, as they provide the right kind of information. Good luck and I hope that I have been helpful.

Sincerely. Alan Schuster, 5/24/2006

► Doesn't Add Up?

Dear Alan, I have been reading different things about nitrates, and I'm still not sure what to do. Our pool was tested a month and 1/2 ago for nitrates and phosphates and both tested over 1000 ppm. We tried a chemical to remove Phosphates and it still reads over 1000. Is the best thing to do to empty half the pool and refill it before we close the pool for the winter ? Do we also add a bunch of chorine to the 1/2 of the water that remains before we refill ? We have had no sign of algae in all this time, and only started putting more chlorine in the pool since we've known of the problem. It would be great to have your advice! Thanks.

Sue S., 9/5/2004

Something is not adding up! With those phosphate and nitrate levels, you should be having major problems. Adding some phosphate remover, just won't reduce a level over 1000 PPM. If you pool is 10,000 gallons that means that there is more than 80 pounds of phosphates and 80 pounds of nitrates in the water. Adding a dose of a phosphate eliminator would barely make a dent. Unless your pool has been filled with water that has been agriculturally contaminated, I doubt that the levels could be that high. Replacing half the water would still leave the water unacceptable. What are the levels in the replacement water? I suggest that you have the pool water and tap water tested again. You might even want to have another dealer do the testing. If you are not having algae problems and not having difficulty maintaining an adequate level of Free Chlorine, you may not have a problem. Winterizing the pool in the normal manner and revisiting the issue next spring, would be my recommendation, unless a retest proves otherwise. Replacement of water is the only remedy for nitrates. A level over 25 PPM is considered problematic. I hope that I have been helpful. Let me know what happens!

Sincerely, Alan Schuster, 9/5/2004

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