I'm building a pen right now, I'm still waiting for the wire to come. It's going to be 16ft wide 23 feet long, and 12 feet high. I want to get some wood ducks, hooded mergansers, and canvasbacks. I plan on putting two ponds in, my question is how do I keep them clean? What can I use as a filter that will keep the water clean and clear, that's not going to cost me several hundred dollars?