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Understanding Ammonia Toxicity


What is a toxic Level of Ammonia?  

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  1. 1. Assuming the following parameters are shown by normal testing methods: 1 ppm (not 0.1) ammonia, 0 ppm nitrate, 15 ppm nitrate, and the water temperature is 73 deg. F, with a pH measuring 7.8, is this a toxic condition for fish?

    • Yes
    • No

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Recently, I created a poll to illustrate some widely held misconceptions about the primary source of ammonia production in a freshwater aquarium.

Now, I’m curious to know how many really understand the levels of ammonia that can be harmful to fish.

Take the poll, and explain your answer.

Edited by tonyjuliano
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While it's worrying . . . I think that it may be quite stressful, but not necessarily toxic. The readings of 0 ppm nitrite and 15 ppm nitrate indicate a cycled tank with this reading indicating an ammonia spike. Unless it dramatically increases, the ammonia surge should be dealt with by the aquarium's bacterial colony. There is, however, a relationship between pH and ammonia toxicity. Somewhere down below 7.0 (maybe 6.4?) Ammonia turns to Ammonium, which is less toxic -- but will still read as high ammonia on titration tests.

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Not for healthy, hardy adult fish. It can be stressful to sensitive fish or to young fish but total ammonia readings have to be quite a bit higher before the un-ionized, 'free' ammonia becomes toxic. Only a low percentage of total ammonia readings contributes to free ammonia, even at higher pH levels (though the higher you go, the more free ammonia).

No need to hit the panic button but there is a need to work to control the spike. Unless you're me, then you'd panic immediately at 1.0 readings, water change with prime, and watch your precious water children like a helicopter parent.

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On 6/24/2021 at 8:40 AM, laritheloud said:

Unless you're me, then you'd panic immediately at 1.0 readings

This would be the reaction that most people have been conditioned to have, and the primary reason for this post - to dispel common misconceptions.

It is generally accepted that ammonia measuring in amounts as low as 0.05 ppm are seriously toxic, which is a VERY small amount indeed.

But... ammonia comes in two "flavors".

In water, ammonia occurs in two forms, which together are called the Total Ammonia Nitrogen, or TAN. Chemically, these two forms are represented as NH4+ and NH3. NH4+ is called Ionized Ammonia because it has a positive electrical charge, and NH3 is called Un-Ionized Ammonia since it has no charge.  This is important to know, since NH3 (Un-Ionized ammonia), is the form which is overwhelmingly toxic to fish. 

The level of ammonia represented by testing methods (liquid titration or strips, it doesn't matter) is the TOTAL amount of ammonia present, not an accurate representation of the toxic level.

It's also important to know that both Water temperature and pH will effect which form of ammonia is predominant at any given time in an aquatic system.  To determine true toxicity, a calculation needs to be made, which is possible using the data in the chart below:


If you follow the chart, you will know that in our stated example, where 1 ppm is the TOTAL ammonia level (usually presumed to be very dangerous), the reality is quite different.

What needs to calculated is the product of total ammonia measured times the factor listed.  In this case 1 X .03 = .03 toxic ammonia.

At a water temperature of 73 deg. F, and a pH of 7.8 then the true level of toxic ammonia is 0.03, not close to the "threshold" of 0.05 ppm at all.  Any decrease in pH and/or temperature reduces this level even further.

If such a condition was present in one of my tanks, the action I would take is to lower the temperature, in lieu of a mad dash for a water change, or worse even, the application of any "ammo-lock" chemical.

The water change will reduce the ammonia, but also carries with it the possibility of disrupting the biological filtration system in place as well as overly stressing the fish.  "Ammo-Lock"?  A poor solution to a problem that doesn't really exist in this scenario, as any ammonia it "locks up" will be released as toxic form again in a short period.

Edited by tonyjuliano
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