At some point, the pH will crash
Not with ammonia....ammonia is a base, not an acid.
In order to drop the pH you'd have to add vinegar, or another similar acid. Having accidentally done that to a SW
tank, I can say it does effectively kill stuff, but creates a godawful mess in the process - and don't even start me on the smell.
I would suggest drying and then boiling or baking the rocks, and ditch the sand. Not sure how the rocks will react to such treatment. LR
is surprisingly brittle stuff when dry. Rinse the empty tank out with vinegar and then water.