When you say that your ammonia has come back down, where was your starting point? How was the ammonia, nitrite, nitrate readings taken?
I am thinking that possibly the initial ammonia level was too low to fully build stable benny bact colonies in your filters.
Keep in mind, if you are doing fishless cycling you can always just start the cycle again. Pump it up to the wicked jade shade at 5 ppm ammonia and when it is reading 0, the nitrites finnally drop to 0 and your nitrate test will make roodolphs reigndeer's nose look dull in comparison.
I have used between 4 and 5 ppm ammonia as a starting point with excellent success. The nitrate readings are in triple digit by the time the ammonia and later the nitrites hit 0.
If the test was done with strips, I would simply disregard the readings, get a liquid test kit and find out what is really going on in your tak.