The pond is about 1000 gallons and has about 20 goldfish in it. The home is about 35 miles north of Phoenix. I am new to having outdoor fish. Due to the algae problem, i would like to have some algae eating fish such as Plecostomus. However, I am concerned that they will not do well with our winters. I am thinking of getting a pond heater but I do not know how many watts the heater should have.