Firstly, top effort on a pond build.
When I buy my own home....... One day, this is the aquaponics set up I'll be building. Fish? Hmm dunno where ya live but I'm in woody point north side of Brisbane and have an ibc out back with gold fish and platties in there. The platies have been breeding over our "winter" if that's what it's meant to be. Checked the temp yesterday morning after a bit of colder weather and it was still 13.5 degrees. I know I'll have some big arse pleco's in my pond, well hope they would survive it. I would think with the water volume the temp wouldn't drop much, maybe a bubble wrap blanket to go over at night? Maybe not... Dunno just ideas coming outa my head. Looking forward to seeing it running that's for sure.
What's the build costs up to so far?
Where are you situated in oz?
How thick is the glass?