It takes a minimum of twenty-four hours to stale water enough to become relatively safe to put fish in, and even then, the only thing that you've done is allow the chlorine to evaporate. It will still contain some heavy metals, chlorimine, and other harmful substances that most dechlorinator removes. Boiling doesn't remove any chemicals from the water, unless you're collecting the steam from it, condensing it, and therefore making it distilled.
