I listened to all the pros and cons of open vs closed systems. Then I decided which way to go based on logical(to me) reasoning and my circumstances.
Closed system:
Once the loop is closed there is little chance of contamination from pond or ground water. The fluid (distilled water and anti-freeze designed for Geo systems) protects the piping, pumps and compressor.
A closed system of loops on the bottom of the pond can be floated up and repaired if something ever goes wrong.
The Pond has reasonably stable bottom temperatures.
