If the second population is much smaller then the bacteria will die off to match the new bio load.
In dying off they are supplying some (not much) ammonia to the remaining bacteria.
But you will not notice this, since they are used to dealing with a much higher bio load, and the die off is not so fast at to overwhelm the ones that are left.
In dying off they are supplying some (not much) ammonia to the remaining bacteria.
But you will not notice this, since they are used to dealing with a much higher bio load, and the die off is not so fast at to overwhelm the ones that are left.