Hello, our pond is still being worked on, but it's about 80% done. Initially, we wanted a pond/waterfall for the sound, but now would like fish. I know we have to put some plants in the pond, but I'd like to know if we need a filter and what kind - also, how should it be connected. You can see in the pictures that we have a pump that takes in water from a bottom drain and feeds a larger center waterfall and two side waterfalls. Is there an inexpensive option that I can add to filter the pond, keep it clear and safe for fish? Thank you!

