Aerobic bacteria suck down oxygen like no tomorrow.

And, um, Aerobi means?

Air-breathing. Your pond is alive with them, they break down
waste. But they need oxygen to live.

If not, leave that bubbler on all the time.

Will do.

The bubbler forms a small current, moving water from the bottom
of the pond to the top. The top of your pond aerates the water
very well, but the bottom of your pond is very low in oxygen.
So you move the low oxygen bottom water to the top, it gets
oxygenated.

The air bubbler itself adds a little oxygen also, but really
plays second string to the circulation/top of your pond thing.

Some folks pull water out of the bottom of their pond, pump
it to a waterfall or something.

A well designed pond will often have two pumps. One to power
the skimmer (to get floaters off the top), and one to circulate
lower water, to oxygenate the pond.

You don't really need a bubbler, if you have the right set up,
but it will work okay if you don't.

How big is your pond, how many gallons per hour is your current
pump?

C//