Dear Mwaba, You can try ...

Dear Mwaba,

You can try Activated glass media Filter of Dryden Aqua, UK.   Discuss with them , ask for their help ,send them sample for conducting trial at their lab. If successfully done, you can buy a filter for its 10 years or more life usage without replacement of media. You can go through case studies published on Dryden aqua website for further clarification.

Activated glass media has very high surface area and NSF certified for drinking purpose use. It is a low cost solution without any chemical addition.  Check with them of they could be of help. For further clarification and best output result I insist to add installation of Activated carbon filter.

First take lab trial, If you don't get your problem sorted out with the above mentioned please write to me. I have another solution as well.