Nutrafin Cycle works well; some of the others, not so much. I've experimented with a few different brands. I'd stay away fom the in-store brands from the big chain stores.
I was a little skeptical at first. It says ya can add fish immediately, so I followed the directions and added a few zebra danios immediately. Followed the directions the next two days. Never lost a fish, never saw any ammonia or nitrite spikes, and nitrates started showin' up at detectable levels a few days or a week later, don't remember how long it took. Anyways, made a believer outta me.
WYite