As an alternative, use dry ice in bowls of water. The CO2 sublimates and carries the water with it to make an awesome fog. It's cold, and hugs the ground for a really eerie effect, while still allowing you to see around the room. It makes a thicker whiter fog that looks a lot more like the real thing (because it IS the real thing). Plus, the CO2 is completely non-toxic, so long as you don't build up so much you suffocate folks. I seriously doubt that would happen unless you have a hermetically sealed home and nobody goes in or out and you make a TON of fog.
The added CO2 is going to make the pH in your tank fall. Perhaps precipitously. But since it will stay close to the floor, it may not make it into the tank so much. I would try to keep an eye on it. No real need to worry unless it starts getting to the mid 7's.
Even so, you would at least have an easy metric on how the fog was affecting the tank, and if things weren't working out you would be able to easily tell. You could then just remove the dry ice from the room and try to air it out.
Plus, it's much much easier on the guests. You can't smell, taste, or even notice the CO2 other than the fog.
