Theres always a chance that plants might bring in some of the right bacteria. Its not a reliable way such that we see people doing it for that but it at least can't hurt. I'd consider big bunches of cheap plants such that you wouldn't mind just throwing them out later if they died or became thick with algae from the ammonia situation. Wish I could see something that made your cycle different than all the others that work ok, sorry! We have one other FC currently, Ape-man's I think, that seems to have this same problem.
~~waterdrop~~