We dont have a ton of money, but want a pond healthy for maybe 4 or so Koi. What is the minimum needed to accomplish that? I will tell you the minimum I know is necessary. 1. At least 3 ft deep. 2. A filter 3. An aerator of some type...bubbler or fountain. 4. Obviously liners, rocks...ect... Other then that, I read alot about skimmers and waterfalls. What can provide a good home now, and asthetics that can be added over time?