I have 5 goldfish, one is 6", another is 5", three others 3" long. I live in CT. My pond is 5' by 7" 300 gals with a deep section 24" deep. Is it safe to winter all the fish or should I put the 3" ones inside for the winter. Can I just run the pump and filter all year long, just shutting down the waterfall, or do I need a heating unit. Thank you.