There are excellent links permanently posted in these Forums about fishless tank cycling. Please read them. It's SO easy to fishless cycle and wayyyy faster. I'd seriously suggest it. You can buy ammonia at any drugstore.
I admit I wouldn't use Danios or Guppies to cycle, way too fragile. People do use feeder goldfish because they are cheap and major poopers, giving the bacteria something to feed on pretty quick. But I admit I don't think I could use ANY fish for cycling a tank. It just wrecks their health or kills them. I am too much of a softie to be able to do it. Heck, my daughter's friend buys feeder goldfish for her pets because she can't bear the thought of somebody feeding them to bigger fish. Go figure. I guess she's like me, a sucker for a nice set of fins!