Garden Pond Water Nitrites

There Is A ZERO Tolerance When It Comes To Nitrite Levels In A Pond!

If Your Test Kit Reveals The Presence of Nitrite … Look At Your Bio-Filtration Equipment

You need to maintain certain parameters in your pond water if you desire to add Koi (or other types of pond fish) to your garden pond. I’ve said this in other articles, but I’ll say it again: you really need to become a “water keeper” rather than a “fish keeper”. If you learn how to maintain “healthy” water, you will more than likely NOT experience many of the completely unnecessary problems that novice and/or unwilling-to-learn hobbyists so often encounter.

What Does A Nitrite Reading Mean?

If your test kit reveals any reading above ZERO it means your new filter has not “cycled yet”. Or, you are overloading an established filter in some negative way. Nitrite is an intermediate chemical metabolite in the “cycle” of the bio-filtration equipment.

A brand new filter will take approximately 6 weeks to completely “cycle”. This means it takes about 6 weeks for the friendly nitrosomona and nitrobacter bacteria to colonize.

In very simplified terms these bacteria process ammonia and nitrite into non-toxic nitrates. These bacteria live, and should happily thrive, in the filter media of your filtration system. Through their efforts, if everything else is maintained properly, you do not have to worry about water quality problems.

However, if you have an established filter and are now experiencing a nitrite reading, you quite likely have a problem in how you have been maintaining (or neglecting) your filter and/or filter media. The problem is causing the friendly nitrobacter bacteria to die off (again, a simplified explanation but sufficient for purposes here). They cannot process the nitrites.

It Is NOT Acceptable To Have A Detectable Nitrite Level In Your Pond Water!

Since nitrite cannot be seen or smelled, your pond water looks just fine. But nitrite can be deadly, particularly to smaller fish. Nitrite damages the nervous system, liver, spleen and kidneys. Koi exposed to low concentrations over extended periods can have long term, irreversible damage. A common indication that a fish has been subjected to a severe nitrite spike is evidenced by the gill covers. They may be rolled outward at the edges and cannot close flat against the fish’s body.

Nitrite also binds the fish’s red blood cells causing gasping and a condition called “Brown Blood Disease”. Koi that die and have widely flared gills most likely have died of Nitrite poisoning.

Don’t underestimate even a low reading of nitrite in your garden pond.

Nitrite Spikes & How To Remedy

What To Do If Nitrites Start To Rise In Your Garden’s Pond Water

How To Handle a Nitrite Spike

Whenever 0.25ppm of nitrite or more is detected in your pond water:

  1. Increase aeration to maximum. For a a nitrite level of 1 ppm or higher, add suuplemental air, if possible.
  2. Stop feeding the Koi if detected in an ESTALISHED pond, reduce amount being fed by half is starting up a new filtration system.
  3. Discontinue use of any UV sterilizers, ozone generators and/or foam fractionators (protein skimmers).
  4. If the nitrite levels is 4.0 or greater, it is highly suggested to transfer the fish to a “safe” holding tank.

Your #1 Line Of Defense Will Be Daily Water Change-Outs. Make Sure To Use Dechlorinator With Each Change-Out.

Water change-out instructions:

  1. Nitirite level is less than 1 ppm: do a 10% change-out and ADD 1-pound of non-iodized salt per 100-gallons of total pond volume.
  2. Nitrite level between 1 and 2 ppm: do a 25% change-out and ADD 2-pounds of non-iodized salt per 100-gallons of total pond volume.
  3. Nitrite level greater than 2 ppm: do a 50% change-out and ADD 3-pounds of non-iodized salt per 100-gallons of total pond volume.
NOTE: Very affordable non-iodized salt can be purchased at big-box DIY or hardware stores. It is sold for use in water softeners. Make sure you do not buy the salt that contains “red out” or has other chemical additives.

The addition of the salt helps reduce the toxic effects on the Koi, but you should only look at it’s use as an interim measure. Address the problem causing the nitirite spike and correct it!

If this spike is occurring in an established filter … you are doing something that is negatively impacting it. Have you rinsed out the filter media recently? It might be so full of waste and goop that the pond water isn’t able to flow through it any longer. Though there are pros and cons against using the pressure from a garden hose to clean off media, I would go ahead and hose it off thoroughly to dislodge all the gunk and reinstall it into your filter.

Make it a point to inspect your filter media at the very least on a weekly basis until you get accustomed to how dirty it gets in what amount of time. Yes, you do have to keep the filter media clean … but not overly “clean”. Remember that you do not want to kill off all the friendly bacteria that reside there, the ones that process the ammonia and nitirites.

If your filter media is getting clogged with waste and such in a few days, I will make an educated guess that you need more filtration and/or better in-pond maintenance. And I will make a wild guess that you might be housing too many fish in too little of gallonage; and you might also have plants in your pond that are contributing dirt that is helping clog your filter media.

I cannot address in this article all the variables I have seen or heard about when it comes to pond and filter problems. I would be able to write 100 pages and still not touch on all the possibilities. But I have tried to give you what “normally” causes a nitrite spike and how to treat it.

Test Your Water Daily Until Readings Return to Zero

Once you get your pond back to acceptable readings, continue to monitor your pond water. Don’t take things for granted … check the pH, ammonia and nitrite levels once a week after you get your pond back on track. Continue to make sure your filter media isn’t clogged with gunk … keep it fairly clean also.

The few minutes it takes to do the tests and check up on your filtration equipment is nothing compared to what you may end up going through by becoming lackadaisical. Besides the hassle of dealing with pond problems, you could end up killing all of your Koi.

Don’t Be A “Fish Fixer” … Please Become A Dedicated “Water Keeper”


  1. Winscene says:

    Excellent article on how to deal with Nitrite problem!!

  2. Claudia Brownlie says:

    Thanks, Winscene! I appreciate your kind compliment. I’ve spent hundreds and hundreds of hours over the years writing all the articles on Artistic Garden! 🙂

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