I'm looking to erect a pond in my south facing backyard in the next three months. My plan is to use a 250-300 gallon galvanized round tub that will sit above ground and have a pergola over it for shade from the direct sun (a shed just west of it will block most of the killer afternoon sun). Now that I have figured out the shade issue, I have questions about what most of you do with your fish/turts during the winters here in Phx, Arizona (or other similar climate). Is it necessary to bring them all indoors or is it fine to leave them outside since we typically only have a few nights that are really cold? Should I invest in a heater? Will the pond residents likely just adapt to the temp fluctuations and be fine?

For more info I plan to keep a male southern painted and likely a male map turtle together in this pond with a variety of small tropical fish (Pencils, Rasboras, Amurs, Corys, Killis, and Mollies) - NO koi or goldfish.

This will be my first pond so any recommendations or comments about what I mentioned above are appreciated!