The water won't do anything as the bacteria we need grow live in the biofilm which is tightly attached to surfaces.
But some of his filter media will help a great deal. He can lose up to a third of it before it affects his tank. Buy him some new media of his choice in exchange
Then put his media in your filter in place of some of your media, preferably at the beginning of the water flow so that any dislodged bits of biofilm will be washed into your new media. Sponges can be cut up to make them fit, or ceramic media placed in a mesh bag.
