no gravel in the bottom of a koi pond.
you need to decide if you want a pond with a few fish like white clouds or gambusa ,
that is built and works different than a koi pond, which is a home for koi which
surprisingly enough become very much pets in a short period of time.
build a veggie filter... there are different kinds, mine is OVER the pond.
http://weloveteaching.com/mypond/mypond.htm
do a google for veggie filters outside the pond.

do you have shelves to hold the lilies?

you also need to consider how you will protect the koi from herons.


On Tue, 09 Oct 2007 12:47:44 -0700, robJ wrote:
I have a backyard concrete pond that measures 12'W x 15'L x 4'D. Until
recently it has been FULL of lilies and a very dense root system,
anchored by substantial sediment. No fish. It has never been filtered
but never had an algae problem because of the amount of vegitation
surface coverage. This year, however we had an infestation of
caterpillar type worms that chewed all the leaves, leaving only stems
and a very ugly pond. I decided to drain and clean it and start over.
This time I'd like to have a few Koi and a more attractive pond. I am
planning on putting about four inches of gravel in the bottom and
replanting just a few of the lilies. My question is how should this
thing be filtered this time? What equipment, etc. for max clarity and
least maintenance