Sorry, forgot aeration in my post. I selected pump and dump for three main reasons over closed loop. 1) Closed loop depends on pond temperature stratification. Any aeration that disturbs this natural stratification will kill your efficiency. Open loop depends on a constant well water temp, which never changes, so efficiency is constant regardless of pond or outside air temp. 2) Closed loop circulates anti-freeze thru your pond. A leak could be a disaster. 3) Open loop can provide water direct from your well to your pond in times of drought.

Downside is maintenance as minerals in well water can eventually clog the unit and it will require periodic cleaning.

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