Yep,you have all Kinds of beneficial microorganisms in that Kind soil that really help take care of your plants health, so you only want to ad organic substances that won't harm them. That is one reason they say not to water with chlorinenated city water as well.
Back when I was on city water, I started letting my water sit for my plants, like Urbz said, it helped a lot, then I got to thinking, well, if the chlorine is bad for my plants, what about me? So I started filtering it, wow, what a difference that made!! The headaches, and stomach aches I was getting ALL the time, went way down.