"The presence of ammonia in aquariums can be a source of many problems. Generally, the amount of ammonia should not exceed 1.2 mg
/L. Levels up to 1.2 mg
/L in very alkaline water (above 8.0 pH) are quite toxic to aquatic organisms."
Ammonia can be present in two forms. Ammonia NH3
, which is a toxic gas, and ionic ammonium NH4
+, which is much less deadly. The pH of the water is the major factor that determines the ratio of NH3
+. When the pH is high, the ammonia is in its toxic form. Toxic ammonia will increase exponentially with increasing pH levels and temperature. A pH value of over 8.0 causes a corresponding rapid increae in the toxic ammonia component." - Hagen Ammonia Test.
The fishs should be fine in the lower pH if kept above 7.8, usually when an aquarium is new the pH is low and fishs seem to appear okay. Inverts and Corals on the other hand need the pH to be around 8.2.