Fish Pond Blues

Argh. The mechanics of a fish pond is giving me a headache. I am designing by myself, a fish pond for my new house. It's not just a rectangular hole in the ground, there's more to it than that. My pond tentatively will be 12 feet in length, 7 feet width and 6 feet depth of which 4' is dug down and 2' is built up above ground. Of the 2 feet built up, only one foot will have water. I'm not sure about aesthetics but building up the 2 feet is definitely safer. Ponds at ground level have a certain notoriety in having people and animals falling in. My parents' front pond has claimed every single dog we've had (till they learn it's there) and a certain number of children.... including myself!

My headache is the filter. I don't know the pond volume to filter volume ratio for a comprehensive pump driven filter. It's causing me a headache in the design as my first design showed its glaring errors when I drew it out. To by pass the need for an extensive filter system I was going to use two cannister filters which could filter up to 1000 gallons each. Here's the trouble, I had them designed sunk down to fit level with the 2 foot build up. Once looking at an actual diagram of it last night I realised that the outflow works on gravity i.e. they need to be higher than the surface of the water. Crap crap crap.

Back to the drawing board.