When will my fish stop scraping his body against the rocks?

The old water mixing with the newer water helps the ich to breed even more and the fish scraping itself against the rocks is only the beginning stages of ich. And as far as my experience with fish diseases go , ich can kill a fish quickly , you can either treat the water immediately with medicine or do at least a 75% water change plus treat the water to be on the safe side and clean the gravel too.