does API test kit can differentiate between ammonia and ammonium?

[giar]

short story, i checked my friend's tap water parameter, it has like 5.3 ph and it reads 4ppm for the APU ammonia chart.. after 3 hours we checked the ph went to 6.2 and the ammonia still reads like 3 something pph..my understanding low ph we will have ammonium not ammonia..

anyone can clarify this?

 

[Beetlebug515]

My understanding, which is fairly limited, is that at lower ph ammonia starts to convert to ammonium but I don't know what the rate of change is. I.e. @ 6 ph 80% ammonia, 20% ammonium? Not sure. I speculate that this is the case, as I run one of my tanks with a very low ph of 4.7-5 and the tank still produces nitrates as any other tank would indicating the presence of ammonia.

 

[Beetlebug515]

From Google, it would seem that at the range we aquarists typically operate, it doesn't make much of a difference.