Sources
In aquaria and ponds the principal sources of ammonia are:
- excretion by fish and other livestock as a normal part
of their metabolism;
- the breakdown of protein in uneaten food or dead livestock
which remains undetected;
- areas of biological filters deprived of oxygen may break
nitrates down to ammonia
It is therefore of great importance that careful cleaning
is undertaken at suitable intervals to remove sources of ammonia.
As ammonia is released into the water by either of these
processes it may take one of two forms:
- Free ammonia (unionised ammonia, chemical symbol
NH3). This form of ammonia is highly toxic to fish
- Ammonium (ionised ammonia, chemical symbol NH4+).
This form of ammonia is virtually non-toxic to fish
| NH3 |
dissolves |
NH4+ |
+ |
NH3 |
| total
ammonia |
Free
ammonia |
Ammonium |
The balance between free ammonia and ammonium
is determined by the pH and temperature of the water and may
be summarised:
| High
temperature
High pH |
Dangerous to fish |
High free ammonia
(Low ammonium) |
| Low
temperature
Low pH |
Relatively safe for fish |
Low free ammonia
(High ammonium) |
Measurement of ammonia
Test kits and electronic meters usually
measure all ammonia present, this is total ammonia (some of
these measure Ammonia-Nitrogen (N-NH3) a conversion
factor being applied to the result to obtain a true Ammonia
reading: full instructions should be available with the test
kits used).
Total ammonia = free ammonia
+ ammonium
Safe levels of ammonia
We recommend that the free ammonia
level be maintained below 0.02mg/l (ppm) in freshwater and
0.001mg/l in seawater. To achieve this the total ammonia reading
should not exceed the values given in the table below.
Levels of total ammonia (mg/l or ppm)
that maintain free ammonia at or below 0.02mg/l at a range
of pH and temperatures:
|
Temp ° C |
pH |
| 6 |
6.5 |
7 |
7.5 |
8 |
8.5 |
9 |
| 0
5
10
15
20
25
30 |
250
54
105
74
50
35
25 |
77
50
34
23
16
11
8 |
24
16
11
7.5
5
3.5
2.5 |
7.7
5
3.4
2.3
1.6
1.1
0.8 |
2.4
1.6
1.1
0.75
0.52
0.37
0.27 |
0.78
0.52
0.36
0.25
0.18
0.13
0.1 |
0.1
0.07
0.05
0.04
0.04
0.03
0.03 |
These figures apply to freshwater.
To meet criteria for marine fish these figures should be halved.
To determine if a particular level
of total ammonia is safe:
The pH and temperature
of the water sample must be known
so that the above table may be used.
IDEALLY TOTAL AMMONIA
SHOULD BE ZERO
This target should be achieved in
the domestic aquarium or pond. Fluctuations are likely to
occur in commercial conditions because of the relatively rapid
changes in stocking density.
Reduction of high levels of ammonia
Levels can be reduced by any, or a
combination of the following:
- lowering stocking density
- reduce feeding
- improve general husbandry
- improve biological filtration use of ion exchange materials
to remove ammonia selectively
- dilution by water change
