Ph & Ammonia

  • Published: March 1st, 2011
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Ph & Ammonia

Understanding the Relationship of pH and Ammonia in the Aquarium

PH levels strongly affect how dangerous ammonia and nitrites become in your aquarium. First let’s talk about what pH is and then work to better understand how common toxins like ammonia and nitrite are affected by pH.

What is pH?

PH [Power of Hydrogen] is a measure of how acidic or basic your water is. It is measured in a logarithmic scale with 0.0 being the most acidic, 14.0 being the most basic and 7.0 being the neutral point. Most tropical fish thrive at a pH level closest to their natural environment. For instance, Discus survive best in acidic water with a pH around 6.5 while African Cichlids prefer much more basic water with a pH of about 8.5. Betta splendens can adapt to a range of pH levels but a neutral to slightly acidic pH best mimics their natural environment.

pH Scale

What Are We Measuring?

When we measure the pH levels we are counting the amount of hydrogen (H+) and hydroxyl ions (OH-) present in the sample. An increased level of hydrogen ions [less bonded] means the sample will be more acidic. When less hydrogen ions (H+) and more hydroxyl ions (OH-) are present [more bonded] the sample will become basic instead. When both the hydrogen (H+) and hydroxyl ion (OH-) levels are about the same the sample is neutral.


What Does it Mean to be Logarithmic?

A logarithmic scale measures ten-fold. Aquarists often forget how important this is when tampering with their pH levels. This means a pH of 6.0 is ten times more acidic then a pH of 7.0 and a pH of 5.0 is then 100 times more acidic then that 7.0 pH level. Once you understand this you realize it is often safer to keep the pH stable even if it is a little outside of the desired range. Once aquarists begin shifting their pH up or down, especially quickly, they tend to experience greater instances of illness or sudden death among their fish. The rule of thumb is keep any pH fluctuations down to less then 0.2 within a 24 hour period to avoid stress induced by rapid or severe fluctuations.


How Does pH affect Ammonia Levels?

Aquarium Test Kit

Aquarium Test Kit Photo by: Xxrobot

You may have heard that ammonia becomes increasingly more toxic in basic water. This is quite true and the reason goes back to those ions mentioned earlier. There are two types of ammonia ions. The most dangerous is (NH3) or ammonia that is unionized. Ionized ammonia is called ammonium and is represented as (NH4+). Ammonium is far less dangerous to aquarium fish. When you purchase an ammonia neutralizer like Kordon’s AmQuel, it acts as a binding agent turning dangerous ammonia into ammonium.


How Does Ammonia Convert into Ammonium? [and back again]

In acidic water ammonia ions (NH3) react with water to create ammonium ions (NH4+) and hydroxyl ions (OH-). When water is basic the reaction goes the opposite way because, as mentioned earlier, there is already an abundance of hydroxyl ions present in basic water. Instead of creating ammonium (NH4+) out of ammonia (NH3) and water (H2O) they hydroxyl ions (OH-) split from ammonium (NH4+) to create ammonia (NH3) and water (H2O).


What Does All This Mean?

What this means is, in basic water (pH higher then 7.0) it’s possible for less harmful ammonium to convert into dangerous ammonia. If you pH is basic you will have to be more diligent regarding your water changes and water-testing regimen. To avoid possible ammonia poisoning cycle your tank and always keep your ammonia level at 0. If you have acidic water don’t think you get off that easy. Ammonia is a serious killer and even at low levels it can cause irreversible damage or death to your fish. You too should be testing your water regularly, keeping up with water changes and keeping your ammonia levels at 0.


  • Eden, Jack. © 2004. Online. Internet. 03-29-05. <>.
  • FishDoc. FishDoc Home of Fish Health. © 2004. Online. Internet. 03-29-05. <>.

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