I can't say for sure what is going on but it seems to have no significant effect on beneficial bacteria in the gut. If you read the recent posts on Bruces site you will see several posts relating to this.
One possiblity is that is absorbed before it can do any harm but this seems unlikely
I did see another theory relating to this but I cant remember where it was.
I myself have seen no bad effects so far but I have remained at 3 drops to try out a zapping device as well