This is interesting.
I was searching ammonia in aquariums and came across a thread discussing ammonia spikes after adding plant fertilizer.
According to the discussion, the Aqueon plant food he was using did not contain any ammonias, but when adding some drops to water in an API test tube and testing, the water went from 0 to 4ppm.
I have been using SeaChem Flourish Advance since adding the plants.
I just did an ammonia test to the tank I have with nothing but water and plants in it... and the plant food.
Same reading as my other tank with the substrate and plants, 0.25ppm ammonia.
So I guess we know where the slight increase came from.
I'm going to stop dosing the tank I'm trying to cycle and see if it goes back to zero.