Filters are by design, meant to remove minerals among other things. The quality of the filter has a lot to do with what it will take out. My system is for particles all the way down to less than a micron.
As for adding minerals, when ever you feed your fish, you are adding some. However, most LFS sell mineral mixes, though they are not always called that. Just read some bottles and you will find them.
As for the PH issue, there are chemicals for that too. I am not in the position to know how they work out since I don't need them. My belief from reading some of the posts on this board is that they can be pretty hard on fish too sometimes.