I'm certainly no expert but I've found thru experience that fish are tougher than you may think. My first "pond" adventure was an old whiskey barrel that I sunk halfway into the ground, filled with water,some plants I potted up from the local marsh and some dimestore goldfish. All lived thru the zone 7 winters where it seemed they were frozen solid. The whole system finally expired during an August extended vacation. Now I have 2 waterfall/pond systems I supervise at work and last week had to drain and fill one due to excessive algae buildup (my fault). I just emptied the pond thru the pump until I couldn't go lower and filled the thing back with city water from the hose.Not only did all the original fish do fine,but I found they had been getting busy in the cloudy water and we had about 2 dozen more little fish than we started with. Sometimes the experts have more advice than you need.