I'd add more ammonia once nitrites also drop to zero and see what happens?
As you know once both ammonia and nitrites drop to zero fairly quickly after adding more ammonia, you should be cycled and ready to add fish.
Are you seeing any nitrates yet?
My experience has been that even though the system is cycled, initially the ammonia and nitrites might tick up a little after you add fish until you have a mature stable large population nitrosomonas and nitrobactor bacteria.
There's lot to be said for a colony of bacteria that have been around for a while. I no longer start new ones for the schools partially for that reason. I bring live colonies on the media.
If pigs could fly bacon would be harder to come by and there would be a lot of damaged trees.
