Since your pond is shallow you will probably want to bring your godlfish and tadpole indoors. Recommended depth for overwintering is 3 feet below the ground surface.

Before the first frost you'll want to cut your water lillies close to the surface of their potting medium and make sure they're submerged underwater.

If you want to keep your fish outdoors (I don't know what's best for the tadpole) there's a few things I'd recommend.
What I did for my shallow pond is added a large piece of styrofoam that covered almost half of the water surface, this gives the fish something to hide under as well as keep some warmth in. I also added a cattle warmer, a disk shaped heater designed to keep a water trough from freezing completely over.
This has gotten my fish through 3 winters so far.

You won't need special aeration during the winter since the warmer the water the less oxygen is available, the heat of summer is when you want the most aeration.

As far as covering completely, I wouldn't recommend as it will trap the gases emitted from fish feces and decaying vegetation. You will, however, need to make sure that you remove all falling leaves and other vegetation throughout the fall and even in the winter months since the wind can often carry leaves and debris into your pond.

Watch your pH and before the winter months arrive make sure none of your fish have an wounds on their body, if they do you will need to treat them...heck, if they do, get them inside into a warmer environment anyway.

Good luck!

Dark-Lotus

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