Backyard Aquaponics
A place to discuss aquaponics

Un-ionized Ammonia - Once the concentration of total ammonia-nitrogen is
known, the amount of toxic, un-ionized ammonia can be calculated and reported in mg/l.
Simply refer to a table (provided with your water quality kit) that gives the percentage of
un-ionized ammonia for different pH and temperatures. Find the percentage value for
your pH and temperature, and multiply this by the total ammonia-nitrogen value (see the
instructions in your water quality test kit for examples). Un-ionized ammonia levels of
0.2 to 2.0 mg/l will stress your fish causing depressed feeding activity. Levels higher
than 2.0 mg/l can result in death.
You should note that a small change in pH can have a profound effect on the
amount of un-ionized ammonia. At 25°C and a pH of 7.0, only 0.40% of the total
ammonia will be un-ionized. While at 25°C and a pH of 8.0, 3.83% of the total ammonia
will be in the form of toxic, un-ionized ammonia.
Nitrites - Nitrites (NO2-) - occur as an intermediate stage in the biological
decomposition of ammonia to nitrates (NO3-). Bacteria in the gravel beds readily oxidize
nitrites to nitrates if oxygen is present. Occasionally there may be an interruption in the
biological processes that convert nitrites to nitrates, and nitrites will begin to accumulate
in the water.
Nitrites should be checked every 3-4 days and should generally be very low (0-2
mg/l). You may notice an increase in nitrites 5-7 days after a “spike” in the ammonia
levels. Nitrite concentrations of 2-10 mg/l stress fish. High nitrites (10-20 mg/l) cause
“brown blood disease” in fish and can result in death (the fish will appear to be gasping
for air at the surface and their blood will appear chocolate in color). Calcium chloride
can be added to the system to reduce the nitrite level.