Question
I have a above ground 300 gallon poly tank that I use for my fish pond.
This is the first season I have had it up. There are about 10-13 koi/gold fish in it. It gets morning sun an after noon shade. It is shade around 2.00 PM. I live in Central IL. I know that I have to take the water fall out before winter to prevent freezing. Do you think that I need to put a heater or a deicer in it. I will be putting a trap over the top for the winter months.

Answer
Dear Janice,

Thank you for your question.
As it can be minus x degrees Celsius I think, the best option is at least cover your pond with a good thick cover.
Heating is also a good option however pricey.
I do not know the depth of the pond, and the more shallow the more easy it will freeze over.
Personally I would do following:
Add heating and ad water circulation pump / aerator and cover the pond.

Good luck and happy koikeeping!

Warm regards,
Raf