this article has lots of info.
Nitrifying Bacteria Facts
check the temp, ph, phosphate level (nitrobactor needs phosphate)
and even though considered a bit crazy and frowned upon today, a little urine does wonders for a cycle.
from the above article;
All species of Nitrosomonas use ammonia (NH3) as an energy source during its conversion to nitrite (NO2). Ammonia is first converted (hydrolyzed) to an amine (NH2) compound then oxidized to nitrite. This conversion process allows Nitrosomonas to utilize a few simple amine compounds such as those formed by the conversion of ammonia by chemical ammonia removers.
Nitrosomonas is capable of utilizing urea as an energy source.
All species of Nitrobacter use nitrites for their energy source in oxidizing them to nitrate (NO3)."
pure ammonia does not contain any urea or uric acid like actual urine does.
don't forget, ammonia is the first by-product of the breakdown of urine.
That is one reason I suspect some fishless cycles stall.
We don't pee pure ammonia.
But check out the article, lots of good info.