Copied from the web.
How pH affects Ammonia
While no ammonia in your tank is desirable it should be noted on what levels ammonia is considered an issue. The ammonia per se is not toxic at low levels but it is not desirable for any aquarium to have detectable levels of ammonia in the tank because it indicates poor filtration in the tank, which is not good for the fish. Ammonia is a slow process for being dangerous to your fish. It is very important to know the pH of your water to determine how fast to proceed with its removal. The ammonia in the water, if left unchecked, can lead to ammonia stress and ammonia poisoning.
Please see here:
Ammonia Stress and Ammonia Poisoning - The First Tank Guide - What Are the Signs of Ammonia Stress?
The common aquarium “ammonia” test measures the total ammonia, both ionized and un-ionized (Total Ammonia Nitrogen or TAN).
The
chronic toxicity, where the ammonia kills slowly by a variety of mechanisms, is as follows:
- 20 to 100 ppm of ammonia TAN at a pH of 6.0
- 2 to 10 ppm of ammonia TAN at a pH of 7.0
- 0.2 to 1 ppm of ammonia TAN at a pH of 8.0
(Of course these numbers may vary depending on where you look on the web)
Any pH between the above numbers you will have to make a linear interpolation. As you can see there is a 10 times increase or decrease in toxicity between pH levels.
A pH of 6.5 will reduce the growth of beneficial bacteria by 90%. A pH of 6.0 will virtually stop beneficial bacteria from oxidizing ammonia to nitrate; hence ammonia may be on the rise.
Ammonia causes internal damage to the brain, organs, and central nervous system. The fish begins to hemorrhage internally and externally and eventually dies.
As you can see it’s a balancing act with pH and how fast your filter(s) can oxidize ammonia. It’s very important that your filter has good effective media that water can flow through all your media and not around your media. Looking at the above if your pH is closer to 8.0, ammonia is more chronic over time and should be handled very quickly. If your pH is at 7.0, low levels of ammonia are not as chronic.
So if you have a pH of 6.0 and you raise your pH to 7.0, the ammonia is now 10 times more toxic. You can see what happens if your filter cannot oxidize the ammonia rapidly. If your pH was 6.5 or lower your bacteria may not be ready to oxidize the ammonia rise quickly.
The natural progression to reduce ammonia is by changing water. So don’t forget your de-chlorinator.
However some de-chlorinators are not the same and will cause issues. Please see here:
Ammonia and Nitrite - The First Tank Guide - Using Chemicals to Remove or Neutralize Ammonia in a Fish Tank
Remember
chronic ammonia is toxic over days and weeks. Chlorine kills in hours.
