Any chance of just leaving them alone and letting nature
take its course? I also had a gadzillion minnows in a
smallish pond (about 200 gallons), along with several
million toad tadpoles and an infinity of snails. My pond
went "balanced" early spring and it has stayed that way, no
bottom cleaning, no filtering, just topping off. Oh, and I
have lots of plants in there.

Now I have considerably fewer minnows, most of the taddies
are gone. I suspect pond predators are taking care of
culing.

Unfortunately, nature isn't being hungry enough for minnows!
Part of the problem seems to be that the minnows kept breeding.
There were thousands of fry from the first batch, and those are
now the same size as their parents-the small percentage that made
it. Still, it probably gives me twice as many as I started with.
Then, there are further groups of progressively smaller minnows,
the largest of which probably number about 50. I have lots of
dragonflies and larvae, but no other predators. The only
predators I've ever had were a family of very destructive racoons
who thought goldfish were tasty snacks and water plants were for
pulling up and tasting. Animal control relocated them to the
country, and they haven't returned. Bull frogs would eat minnows,
but my father had one that was eating his koi. Since my
goldfish aren't as big as his koi and bullfrogs aren't native
to California and are actually an environmental disaster
for native frogs, I won't try that. Any other suggestions?

Also, my pond has no filter or any of that, just 2 solar
pumps to give me some circulation. I had very little
trouble with algae, since the plants use what the algae
wants, until I had all of these extra fish! I'm still
mostly ok, but I'm very worried about oxygen levels this
winter. I figure the minnows would survive better than
my fantail goldfish at low oxygen levels! Therefore, some
of the extra minnows must go!

Monica