I am a definite NO for rocks anywhere and YES for ecosystem. It seems to m
e, however, that there are as many possible systems as owners! Phyllis and
I aimed for cheap, fast and easy.

The main pond is bare bottomed, sloping very gently to a collection point.
Bare bottom allows the fish and flow to move muck to the filter. The lowe
st point is on the opposite end from the return stream, forcing the flow to
move the length of the pond. The low point has a place for debris that wi
ll not fit the filter (intake is 1/2" screened or above the bottom of the c
ollection well. This pulls water from a bit above the lowest point. -Once
a year-, a simple pool net can be used to remove the big stuff.

The water is pumped to a smooth-bottomed veggie filter filled with fast gro
wing floating plants (e.g. hyacinth, water celery, water lettuce). The veg
gie filter should be 10-20% the size of the main pond. The water goes thro
ugh the filter at about 45 min per water change. The plant roots act as me
chanical filters and bacterial surfaces. The plant growth grab nutrients.
The filtration and slow flow allow the muck to settle to the bottom of the
veggie filter. Water exits at the top of the side opposite the water entr
y point and returns by stream or falls to the pond (aeration).

-Once a year-, in the spring before new growth, the veggie filter is draine
d from its bottom. Around here we just pull the plants, put a dome of 1/2"
mesh over the drain, and let the water run out. Most of the muck simply f
lows out. We add a chaser of pond water to flush what will flow out. What
does not drain is netted out with a pool net. Then the drain is closed, t
he plants tossed in, and the filter refilled. Good for another year.

With this model you NEVER have to drain or even sweep the main pond. Annua
lly, you net the big material from the deepest spot in the main pond. Annu
ally, the veggie filters are drained,flushed with pond water and refilled.
We do three veggie filters and the main pond in about 2 hours. That is al
l for the year for a 4,000 gallon system! At this point, the water is clea
r all year and the fish very healthy (2 deaths in 14 years).

The keys: NO rocks in the pond, enough veggie filters, well set drains.