Is it normal that water start to contain nitrites a few days later

[martinmin]

I usually get tap water into a barrel and let it stay a few days. When water is initially poured into the barrel,  nitrite is zero; then I add a few drops of Prime dechololation liquid into it, and let it stay a few days, and test it again, now the nitrite level is quite high. In both cases, I used Aquarium Co-Op test strips to test that. Is that normal? 

Why does the water suddenly get nitrite in a few days? I heard that it is better to avoid using fresh tap water, but waiting for a few days is much better. Is this normal? The reason I ask this is that fishes die in my little tank gradually after I did a water change, and then I tested the water which has stayed in the barrel for a few days. 

 

 

[Galabar]

There have been others on here who have seen their totes leach ammonia.  What type of barrel is it?

[Cinnebuns]

I have aged tap water before but there are very few reasons to do so if you are using dechlorinator. Why are you aging the water exactly?  

In regards to the nitrites, what's likely happening is there is some ammonia present in the water which is being converted to nitrite but since it's not a full cycle the nitrite is not getting converted. Just a guess.