No, you're probably not doing anything. If your water contained organic contaminants or ammonia, this would take some of that out, I suppose, but most municipal supplies don't (though chloramine is a real possibility.) The peat is likely contributing something to the water, but the carbon should be pulling much of that right back out.
Unless you know exactly what is in your water and have a good background in chemistry to know how to precipitate whatever you want gone from it, adding things to your water is going to increase your TDS. Even then, it's probably going to be more expensive than buying distilled.