Ammonia source?

[draveragefish]

I am starting a 20 gallon long planted tank, and was very surprised about the water parameters just 48H after setup and planting. 1 ppm ammonia, 2 ppm nitrite, and 80-160 ppm nitrate. There are no fish and I can see only 1-3 trumpet snails that came along with the plants.

For context; I have eco-complete with 8-10 ez root tabs in mesh bags capped with coarse sand. There are a variety of stem plants, annubias, dwarf sag and java Fern. I added two pumps of easy green after adding the first water. I do have some cycled bio media in a HOB filter. 

I was pleased to see that the "cycle" seemed to have started already, but I'm not sure what was causing such a spike in ammonia so quickly? Any thoughts?

(I did an 80% water change and the plants seem quite happy)

[draveragefish]

Yes. Tap water is 7.0 pH, 0 ammonia, 0 nitrite, 0 nitrate.

[Lennie]

Is there lots of decaying plant matter? 

They wouldn't increase it a lot but would create a bit of reading I guess. It is common for plants to melt when they change forms or water.

[draveragefish]

Definitely a few sad ludwigia leaves. I did my best to scoop out the plant matter after initial filling. I considered decaying plants but wasn't sure if it would cause such an ammonia spike so quickly.

[Colu]

My guess would be the root leeching into the water column