Originally Posted by mikejp67
Let me see if I understand this correctly. If the PH is below 7, I will read ammonia from my test kit but its not ammonia its ammonium? And ammonium is non-toxic to fish? So as long as my PH is below 7, my tank occupants are safe other than nitrites?
Now, Im confused
Basically, yes...to your questions I mean, not to you being confused--though you may be that too.
Ammonia is a form of nitrogen, as is nitrite and nitrate. Dissolved in water, ammonia has two forms: one form is un-ionized ammonia [represented in the period table of elements as NH3] and the other is the ammonium ion [NH4+]. The value reported by our test kits (all but the scientific technical type) is the sum of both forms, what we term total ammonia or simply "ammonia." The relative proportion of the two forms present in water is highly affected by pH and temperature.
Un-ionized ammonia [NH3] is the toxic form and predominates when pH is high. Ammonium ion is relatively non-toxic and predominates when pH is low. In general, less than 10% of ammonia is in the toxic form when pH is less than 8.0 pH units, but this is more than enough to affect aquatic life. This proportion increases dramatically as pH increases.
The equilibrium between NH3 and NH4+ is also affected by temperature. At any pH, more toxic ammonia is present in warmer water than in cooler water. This is another reason for maintaining the aquarium water temperature in the lower end of the preferred range for each fish species.
The chart below from AquariumWiki illustrates this; unfortunately the forum software will not allow extra spaces between text, so the chart is a bit jumbled, but you should be able to decipher it. % Percent of ammonia from 'total ammonia'
Temp C/F pH 6.5 pH 7.0 pH 7.5 pH 7.7 pH 8.0 pH 8.5
20C (68F) 0.125 0.395 1.239 1.95 3.81 11.15
25C (77F) 0.179 0.565 1.766 2.77 5.380 15.242
28C (82F) 0.221 0.696 2.170 3.396 6.55 18.156
30C (86F) 0.253 0.798 2.482 3.78 7.450 20.292
Consequently, at the normal aquarium temperature of 77F, "ammonium" testing at .5ppm will have only .179% in its toxic form, but at a pH of 7.5 it will have 1.766% toxic. This may not seem like much of a difference, but it is.
The majority of ammonia detoxifiers, such as the conditioner Prime, detoxify ammonia by binding it such that it becomes ammonium.