Hi Pixi,

With rocks in the pond the gunk, especially fish poo, settles in between the
rocks and goes sour.
Anaerobic bacteria, bacteria that thrives without oxygen, and gives off an
awful smell. Goldfish and koi are carp, bottom feeders and snufflers. They like
to mess around looking for food and will stir it up and all the nasties down
there with it.
Successful rock lined ponds must be really cleaned every spring. That means
pumping out the water, removing the fish and taking a power washer to the
rocks, pumping out the dirty water, rewashing, repumping, until the gunk is
removed from the rocks.
The demo pond at a nursery here does that every spring. It takes
about three strong young men a good day to do the work.
Most of us find that too much work.
When we cleaned our pond this spring, we pumped out the water, removed the fish
and then my DH and two teenager boys scooped out the muck. Didn't have to slide
around on rocks and it went pretty quickly.
Lots of folks use a shop vac and get the muck out that way. Bottom drains make
it even easier.

With a skimmer and diligent trimming of your dead plants in the fall before
winter sets in you will have a lot less muck to deal with.
A pond's mission is to fill in. The dead plants, the fish poo, the blown in
sand and dirt, the runoff will do the trick.
Our ponds we want to keep a pond longer! So we have to deal with some way to
keep it from filling in.
Bottom drains, skimmers, smooth bottoms and cleaning make it easier to keep
ahead of the muck building up.

If you want to keep the rocks don't put in goldfish and koi. Instead buy some
rosie red minnows, usually sold as feeder fish at petstores. They are light
orange, stay small, easy to see and very playful.
Don't feed them much, if at all, keep their fish waste at a minimum. Trim all
dead plant material before it can sink to the bottom, make sure the skimmer
gets all the leaves or net the pond if you have a particularly heavy leaf fall
this fall.

kathy :-)
k30a