I've had discussions with my brother in law about this issue, and it seems as though the chlorine level in the tap water is not high enough to actually cause a massive disturbance in BB levels, provided the water does not sit on them chlorinated, and comercial declorinators remove the chlorine fast. If the water contained enough chlorine to negatively impact the BB, wouldn't it be bad for us 2? The amount in chlorinated tap water is there to prevent the growth of these sorts of things in the water, not eradicate existing colonies. BTW, my brother in law is a wastewater treatment engineer. Lots of good discussions on bacteria and the denitrification cycle.