[aman74]

AC will pull trace out of the column, so we don't use it unless removing tannins etc. But you can use it as a bacterial medium.

Do you have any info that shows that this is true?

In the above link from the Barr report it's mentioned that if this is true it's effects are minimal.

Ideas seem to get perpetuated without any info to back them up. Not saying it isn't true, I just don't know that it is without more info.