I have a 90g tank which has been running for 3 weeks. After 1 week, I put
in a 1" fantail. Right now,there is the fantail, a baby swordtail (only 3
mos old, and about 1/2" long) and 4 snails (mystery snails I added last
week), and I still haven't seen the ammonia go up either. Maybe if you do
it slow enough, it doesn't spike as high. I have 2 ryukins (1-1 1/2") and
plan to add them slowly as well, one at a time, at least a week apart. They
are still in quarantine until next week, though.

Good luck,
Tammy