~ jan JJsPond.us writes:

why leave out the rock? should I use gravel instead? I like the look of the rock
Roger

You can never get all the crud out that rock collects, if you must have it,
only have one layer, imo. ~ jan

Since koi like to root around I added black aquarium gravel to my pond when
I built it. Nothing collects in it because it is scrubbed in each koi's
mouth at least daily :-)

I used black because I didn't want to see it. If you like the look you
can use regular aquarium gravel. If you do, you will save
much $$ by purchasing at a home supply store. You can get 100#
sacks for $15. All sorts of grades are available.