Here's a Quick Way to Prevent Toxic Ammonia Levels

What is a safe level of ammonia in an aquaponic system?  This question elicits more incorrect responses, confusion and frustration than any other topic in aquaponics.  Why?  Because new growers are not instructed on how to interpret water quality readings together to evaluate toxicity.

Ammonia, when dissolved in water, becomes partially ionized.  The ionized ammonia is called Ammonium \(NH_4^+\) and is not toxic to your fish.  Non-ionized ammonia, often referred to as "free ammonia" (\(NH_3\)), is highly toxic in low levels.  From this you need to know two very important things.

  1. Of the two most common water quality test kits, neither provide a reading of free ammonia.  Instead they provide a reading of total ammonia nitrogen (TAN), ammonium or both.
  2. Free ammonia is a function of \(pH\), water temperature (\(T\)) and \(TAN\).
$$ NH_3(pH, T, TAN) $$
In other words, a free ammonia evaluation requires pH and water temperature in addition to an ammonia reading in order to get an accurate assessment of toxicity - it cannot be determined solely on the ammonia water quality reading. To prevent ammonia toxicity, track and then evaluate \(pH\), \(T\) and \(TAN\) using the calculator below. The question of safe ammonia levels should be interpreted as, "What is a safe level of free ammonia in my aquaponic system?" The free ammonia calculator below uses the following scale, based in part on reports from the EPA:
  • Safe:  \(0 \le FA \le 0.019\)
  • Danger:  \(0.020 \le FA \le 0.030\)
  • High Danger:  \(FA \ge 0.030\)

Did you find this tool useful?  Let us know in the comments below.

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