The most likely reason for having ammonia in one's tap is due to one's water company using chloramine. When chloramine is broken down you get chlorine and ammonia. Dechlors normally handle both chlorine and and chloramine. However, in the case of chloramine the result of detoxifying the chlorine is ammonia. Ammonia is not wanted in an established tank with fish. In a cycling tank we are adding it, and as you did, we can adjust the ammonia dose to account for the tap ammonia.
However, most dechlors today come with an ammonia detoxifier included and this can cause issues when testing for ammonia in terms of false readings. There is a way around this in a tank being cycled fishlessly and that is to use a dechlor that does not contain an ammonia detoxifier. This will break down chlorine and chloramine but, in the latter case, will have no effect on the ammonia produced.
When using Prime one cannot rely on ammonia results for about a day after using it. According to SeaChem "Prime dissipates from your system within 24 hours." (from
http
/www.seachem.com/support/FAQs/Prime.html ) This means you have another option here which is not to test the water for the next 24 hours after using Prime.
If you have 14 hour water and this is all that is treaedt, adding it to the tank will automatically dilute it. So the odds here is you are pretty much safe to do this. What concerns me more than ammonia would be nitrite. You nitrite is kikely over 5 ppm already or soon will be. I hate doing anything that slows the nitrite phase as it takes longer than the the ammonia phase in cycling.
To be safest I would advise you do the following. Wait until your aging water has been doing so for 24 hours before you do anything. Do not add any ammonia to the tank yet. Wait until you have topped it up with the 24 hour water. Then proceed from there. It wont hurt anything if one has to wait a few extra hours before doing the next ammonia dose called for in the directions. I would also suggest that you keep a few gallons of dechlored and aged water on hand or see if you can find a small bottle of dechlor that does not detox ammonia. Either one will make your life easier in terms of needing to add water during a fishless cycle for any reason.
The guidelines for adding ammonia in the cycling directions are designed to prevent problems from having too much ammonia or nitrite. Both the timing and amount to be added should never cause problems in this respect when the directions are followed. However, the key to testing is that 24 hour wait between adding and testing to see how much a tank handles in that amount of time. There is no danger if one tests on a day and finds out it is time to add ammonia but does not do so for another day. The cycle wont stop, it likely won't even slow. And even if it added a day to the total cycling time, this is meaningless compared to dosing too much and/or too soon and stalling or even undoing the cycle.
