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I wanted to explain how ammonia works in aquariums in real life - for beginners and anyone else that is not aware of the science. (There’s some mention of nitrite as well.)
I’m primarily addressing planted and general aquariums though the science applies to all aquariums. In this hobby we tend to think if ammonia as just one thing but it isn’t.
Then most aquarists are told repeatedly from the very start of their journey into this very enjoyable hobby that any ammonia is bad, (or very bad), or a total disaster in the making.
That’s easy, for sure, no explanations needed, nothing to have to wrap one’s brain around, but I don’t think it’s the best way to go about it.
I must confess, I visualize this advice about ammonia being provided by the inimitable Boris Karloff’s monster shouting “Ammonia BAAAD!”
I’ve seen any number of posts online telling those asking about their tank or symptoms in a fish that their fish has ammonia poisoning or ammonia burns, when the reported ammonia levels are nowhere near high enough to bother the fish.
I think it is a disservice to aquarists to oversimplify it to this degree. The reality isn’t all that complicated though I admit it took a little time and paying attention to wrap my own aging brain around it.
First, a few facts.
Dosage always matters.
The majority of ammonia tests are slightly misleading if taken at face value.
I will explain that last one later on.
There is a safe level or dose for the toxic form of ammonia (which I’ll get to).
Anything up to .6ppm is safe, anything from .6 on up is a big problem, where the measure is of pure NH3. So at a reading of .25 or .50ppm there is zero cause for concern.
(I’ll digress for a minute here & mention that nitrite (NO2) has a safe level too, though I’ve yet to find any reliable confirmation for precisely what that level is.)
Some apparently reliable sources say NO2 is safe up to .75ppm, others say .5ppm.
Sadly, none offer any good references for the data. Commonly, .25ppm is cited as a safe level so in the interests of practicing great caution my choice is to assume that the safe level is .25ppm for now.
Fish sensitivity to toxins is variable - what would stress some fish to death won’t bother others.
With NO2, a level that’s high enough to change blood haemoglobin to methaemoglobin (& thus cause breathing problems) in some fish won’t do the same for all other species or even individuals of the same group.
The majority of ammonia tests we use in this hobby are TAN tests (TAN stands for Total Ammonia Nitrogen). They work by first raising the pH of the water sample from whatever it is to about pH12, at which point all the ammonia is in the form of NH3. Then it tells you how much NH3 there is.
There’s no way to determine solely from the test result how much of it might have been NH4 to start with.
That is an important detail because this hobby tends to consider ammonia as just one thing when it’s actually two very different things that share a rather interesting relationship.
NH3 is ammonia, also called free or unionized. It is the one with the eye-watering, nose & throat burning pungent scent.
NH3 easily crosses fish gills and is highly toxic to aquatic life in very small amounts, but as I mentioned at the beginning of this post, it does have a safe level.
Then there is NH4, or ammonium. It is ionized and in pure form it is completely odourless.
Though ammonium is not an inherently nontoxic compound, it is not able to cross the gills of fish and other aquatic life the way NH3 does, which is what makes ammonium nontoxic for fish and other aquatic life.
NH3 & NH4 are two different nitrogen compounds that have a well understood ratio & relationship to each other which is rarely explained or understood in this hobby.
Some aquarists are aware that higher temperatures or pH make ammonia ‘more dangerous’ but again, it isn’t quite that simple and I think if it was better understood, it would reduce anxiety & worry for a lot of aquarists.
The ratio or equilibrium that exists between NH3 & NH4 is primarily controlled by the pH of the water and to much smaller degrees by water temperature (and salinity, if it’s saltwater.)
Simply, the lower the pH is, the more NH4 there will be relative to NH3 and vice versa.
The colder the water temperature is, the more NH4 there will be relative to NH3 and vice versa.
Exactly how much of a temperature change would be a cause for concern is difficult to say but it takes more than a degree or two (either C or F). Even a ten degree F rise in temperature wouldn’t necessarily make all that big of a difference, though it could.
In the average home tank (well, those that aren’t full of African cichlids) with a pH from roughly 8.3 on down, it is quite rare for NH3 to ever rise high enough to cause any problems.
At any pH below about 7.2, there is so little NH3 present that it might as well be zero. By the time pH is a bit less than 6 it’s functionally zero.
Conversely, once pH gets to 8.5 or higher, most of the leeway vanishes. By pH9 there’s barely any left.
Some Examples
If I assume there is a water temperature of 75F, pH of 7.5 and a TAN test reads 10 (yes, ten!) ppm, there’s only 0.1615ppm of NH3.
That’s less than one third of the toxic dose and all the rest is harmless NH4. There is loads of safe leeway.
If I were to raise the temperature in the preceding example by ten, to 86F, with the other two values remaining the same (75F + 10ppm TAN ) there would be 0.3227ppm of NH3, which is just over halfway to the dangerous dose threshold and that still leaves quite a lot of safe leeway.
If I assume temperature is 75F, but pH is a full point higher at 8.5 and the TAN test reads 4ppm, then you’d have 0.5641ppm of NH3 - disturbingly close to the safe threshold but still just on the right side of it.
But if I took that to 5ppm of ammonia then it will be over the safe threshold.
For those whose fish of choice like a higher pH, even at pH9 there’s still a wee bit of leeway, though not much.
If temperature is 75F, pH is 9 and a TAN test result is 1 ppm, then there would be 0.3418ppm of NH3 and the fish would still be safe.
But at a test result of 2ppm, NH3 will be over the safe threshold, though not by very much. Still, it would be very bad news for the fish.
(I do these calculations with a purpose made online ammonia calculator and just for fun, I put in 20ppm - yep, that says twenty ppm, with 75F & pH7.5. There’s still only 0.3231ppm of NH3 even at that level. )
I think you can see why the reading on a TAN test could be considered just a wee bit misleading to anyone who is not familiar with the relationship between NH3 and NH4., especially with the “any ammonia bad” outlook.
There are charts online where you can just look at a graph and determine what amount of NH3 you have, so long as you know pH, temperature and have a TAN test result.
It is my hope that this will alleviate some anxiety for aquarists who have bought into the idea that “any ammonia Baaad!”
An afterthought
When it comes to NO2 - nitrite, it truly is the nitrogen compound to worry about the most if it starts to rise.
Even at levels that are too low to affect blood haemoglobin & breathing in any given fish, it causes stress which worsens as the levels rise.
Plus there is no leeway as often exists thanks to the equilibrium between NH3 & NH4.
So NO2 is a greater worry than ammonia, particularly once it gets past 1 ppm.
I sincerely hope this will be useful to anyone that reads it.
I’m primarily addressing planted and general aquariums though the science applies to all aquariums. In this hobby we tend to think if ammonia as just one thing but it isn’t.
Then most aquarists are told repeatedly from the very start of their journey into this very enjoyable hobby that any ammonia is bad, (or very bad), or a total disaster in the making.
That’s easy, for sure, no explanations needed, nothing to have to wrap one’s brain around, but I don’t think it’s the best way to go about it.
I must confess, I visualize this advice about ammonia being provided by the inimitable Boris Karloff’s monster shouting “Ammonia BAAAD!”
I’ve seen any number of posts online telling those asking about their tank or symptoms in a fish that their fish has ammonia poisoning or ammonia burns, when the reported ammonia levels are nowhere near high enough to bother the fish.
I think it is a disservice to aquarists to oversimplify it to this degree. The reality isn’t all that complicated though I admit it took a little time and paying attention to wrap my own aging brain around it.
First, a few facts.
Dosage always matters.
The majority of ammonia tests are slightly misleading if taken at face value.
I will explain that last one later on.
There is a safe level or dose for the toxic form of ammonia (which I’ll get to).
Anything up to .6ppm is safe, anything from .6 on up is a big problem, where the measure is of pure NH3. So at a reading of .25 or .50ppm there is zero cause for concern.
(I’ll digress for a minute here & mention that nitrite (NO2) has a safe level too, though I’ve yet to find any reliable confirmation for precisely what that level is.)
Some apparently reliable sources say NO2 is safe up to .75ppm, others say .5ppm.
Sadly, none offer any good references for the data. Commonly, .25ppm is cited as a safe level so in the interests of practicing great caution my choice is to assume that the safe level is .25ppm for now.
Fish sensitivity to toxins is variable - what would stress some fish to death won’t bother others.
With NO2, a level that’s high enough to change blood haemoglobin to methaemoglobin (& thus cause breathing problems) in some fish won’t do the same for all other species or even individuals of the same group.
The majority of ammonia tests we use in this hobby are TAN tests (TAN stands for Total Ammonia Nitrogen). They work by first raising the pH of the water sample from whatever it is to about pH12, at which point all the ammonia is in the form of NH3. Then it tells you how much NH3 there is.
There’s no way to determine solely from the test result how much of it might have been NH4 to start with.
That is an important detail because this hobby tends to consider ammonia as just one thing when it’s actually two very different things that share a rather interesting relationship.
NH3 is ammonia, also called free or unionized. It is the one with the eye-watering, nose & throat burning pungent scent.
NH3 easily crosses fish gills and is highly toxic to aquatic life in very small amounts, but as I mentioned at the beginning of this post, it does have a safe level.
Then there is NH4, or ammonium. It is ionized and in pure form it is completely odourless.
Though ammonium is not an inherently nontoxic compound, it is not able to cross the gills of fish and other aquatic life the way NH3 does, which is what makes ammonium nontoxic for fish and other aquatic life.
NH3 & NH4 are two different nitrogen compounds that have a well understood ratio & relationship to each other which is rarely explained or understood in this hobby.
Some aquarists are aware that higher temperatures or pH make ammonia ‘more dangerous’ but again, it isn’t quite that simple and I think if it was better understood, it would reduce anxiety & worry for a lot of aquarists.
The ratio or equilibrium that exists between NH3 & NH4 is primarily controlled by the pH of the water and to much smaller degrees by water temperature (and salinity, if it’s saltwater.)
Simply, the lower the pH is, the more NH4 there will be relative to NH3 and vice versa.
The colder the water temperature is, the more NH4 there will be relative to NH3 and vice versa.
Exactly how much of a temperature change would be a cause for concern is difficult to say but it takes more than a degree or two (either C or F). Even a ten degree F rise in temperature wouldn’t necessarily make all that big of a difference, though it could.
In the average home tank (well, those that aren’t full of African cichlids) with a pH from roughly 8.3 on down, it is quite rare for NH3 to ever rise high enough to cause any problems.
At any pH below about 7.2, there is so little NH3 present that it might as well be zero. By the time pH is a bit less than 6 it’s functionally zero.
Conversely, once pH gets to 8.5 or higher, most of the leeway vanishes. By pH9 there’s barely any left.
Some Examples
If I assume there is a water temperature of 75F, pH of 7.5 and a TAN test reads 10 (yes, ten!) ppm, there’s only 0.1615ppm of NH3.
That’s less than one third of the toxic dose and all the rest is harmless NH4. There is loads of safe leeway.
If I were to raise the temperature in the preceding example by ten, to 86F, with the other two values remaining the same (75F + 10ppm TAN ) there would be 0.3227ppm of NH3, which is just over halfway to the dangerous dose threshold and that still leaves quite a lot of safe leeway.
If I assume temperature is 75F, but pH is a full point higher at 8.5 and the TAN test reads 4ppm, then you’d have 0.5641ppm of NH3 - disturbingly close to the safe threshold but still just on the right side of it.
But if I took that to 5ppm of ammonia then it will be over the safe threshold.
For those whose fish of choice like a higher pH, even at pH9 there’s still a wee bit of leeway, though not much.
If temperature is 75F, pH is 9 and a TAN test result is 1 ppm, then there would be 0.3418ppm of NH3 and the fish would still be safe.
But at a test result of 2ppm, NH3 will be over the safe threshold, though not by very much. Still, it would be very bad news for the fish.
(I do these calculations with a purpose made online ammonia calculator and just for fun, I put in 20ppm - yep, that says twenty ppm, with 75F & pH7.5. There’s still only 0.3231ppm of NH3 even at that level. )
I think you can see why the reading on a TAN test could be considered just a wee bit misleading to anyone who is not familiar with the relationship between NH3 and NH4., especially with the “any ammonia bad” outlook.
There are charts online where you can just look at a graph and determine what amount of NH3 you have, so long as you know pH, temperature and have a TAN test result.
It is my hope that this will alleviate some anxiety for aquarists who have bought into the idea that “any ammonia Baaad!”
An afterthought
When it comes to NO2 - nitrite, it truly is the nitrogen compound to worry about the most if it starts to rise.
Even at levels that are too low to affect blood haemoglobin & breathing in any given fish, it causes stress which worsens as the levels rise.
Plus there is no leeway as often exists thanks to the equilibrium between NH3 & NH4.
So NO2 is a greater worry than ammonia, particularly once it gets past 1 ppm.
I sincerely hope this will be useful to anyone that reads it.
