hi there!
welcome to bristlenose world

i too have peps that im trying to breed. i have tried everything i have read to do, but sometimes you just gotta leave them to themselves and hopefully in their own time they are ready to breed. don't give up though!
your triggering technique seems a little extreme by dropping the level to 25% of the tank and then re-filling it up. to me i would be worried about cycling the tank all the time and getting high ammonia readings etc.
usually the common triggering way for bn is:
-increase temp to 28 degrees for a week
-wait til there is a drop in atmospheric pressure (or about a week if you don't want to wait)
-do a big cold water change of 40% and drop temp to about 20 - 22 degrees.
-leave them alone for a few days and hopefully the spawn.
that's a very brief description.
have you tested your water recently other than nitrate? btw, others can correct me if im wrong, but a i'd be worried having a 0 reading of nitrate, i've always been told to have at least a small reading of 5 - 10.
how long have you had them? perhaps they just need to settle in for a few months first.
purchase Doug's bristlenose ebook online for heaps of info - it's a great read and i have learnt heaps from it

hope this helps

and let us know how it all goes