Thank you. The person that was insisting that water changes significantly reduced the levels of beneficial bacteria in the aquarium used this article to "prove" her point.
The point that she was making, is that by doing a 25% or larger water change in a mature system, would deplete the "beneficial" bacteria in the system, resulting in catastrophe.
Very large water changes can cause problems by exposing live rock to air, and killing organisms on it. The decay can then cause an ammonia spike, if enough biomass is involved.
The bacteria die-off would be slow. Some organisms, like certain sponges, will die on contact with the air, though, and if there's enough decaying biomass, the tank can have a bad ammonia spike.Any idea how long it would take before the bacteria would die off?