Ammonia Spike

[Otter2009]

I recently trimmed a bunch of floating water sprite and cleaned some dead leaves on other plants throughout my tank. Afterwards, I noticed that the ammonia had spiked to 1.0ppm. Was this likely caused by me trimming and cleaning or is there something else I should be concerned about?

 

[Otter2009]

As a quick followup, my ammonia levels have dropped back to 0 (as well as my nitrite and nitrate levels) but my fish have been swimming at the top a lot today. Any ideas as to why?