It's #1 because the members here focus on serious and competitive koi keeping. Time and space are not wasted on water gardening, etc. If you want to compete, this is the place to learn. I do enjoy other sites, but I take them for what they are, and nothing more. When I want to sit down, read, and do heavy duty learning...this is where I stay.
I remember when I started here a few years ago. I already had won a few awards and thought I was hot s--t. I posted pictures of my fish here...and subsequently got torn apart. I said to myself, this is where I have to be. This is where I am going to learn. Several years later and I realize I have only scratched the surface of this hobby. I can't say enough good things about this site... It is an excellent resource for those who are serious about koi. Thanks for the education!!!