pond about 2000 gal , and close to 4 ft. deep, running skimmer to waterfall and a pump in pond to stock tank filter planning on shutting down skimmer pump to fall and bringing in,and shutting down the stock tank , would it be a good idiea to let that pump run and divert water directly at pond surface to help keep from freezing? or just bring that pump in doors too and use a heater to keep a opening in surface? what about the bio-filter being shut down? thanks