For a pond that size you'd be fine going with a model 13-AUV040 sterilizer. It's rated for ponds between 1200 and 2200 gallons. It's rated to handle a maximum flow of 2900 GPH. Be sure that you don't run water through your filter too fast. Remember that too much flow through a filter can be just as bad as too little. Your nitrifying bacteria won't have enough time to go to work on the ammonia and nitrites in your water. Pay close attention to getting a filter that's properly sized to your pond and also pay close attention to how much flow it's designed to handle.