Planted Tank Guru
Join Date: Jun 2004
Location: Baton Rouge, LA
Without knowing what the active ingredients in Prime are, it's really impossible to speculate what it does with the heavy metals, or for how long. Better to ignore this aspect of it.
Most heavy metals are beneficial in appropriate quantities. There's no need to detoxify them unless you know you have an excessive amount, in which case I'd set to work trying to eliminate them by never adding them.
As for ammonia, I consider Prime to decay to zero over a 48 hour timespan. For much of the first day, it will probably bind all the ammonia, because it's added in excess. After that, it will start releasing it. Not a concern though, unless you have no biofilter/plants to take up the ammonia. The normal purpose is to bind the initial spike that occurs with a water change, with water containing chloramine.