Your settling tank is another smaller pond next to your main pond. Your pump sucks from the settling tank, and a big open pipe connects the two ponds. The water from the main pond flows through the pipe to the settling tank as the tank's water level is drawn down by the pump, because two bodies of water connected thusly will always try to remain the same level.

So the water flows like this: From the main pond, through the bottom drain to the settling tank, then to the pump usually through some kind of brushes or mat to help filter out debris and critters (mine is a black box with brushes in it, sitting underwater). Then the water goes from the pump to the UV light, if you want one, and then to your biofilter, which is often the head of your waterfall back to your big pond.

That's one way to do it that works. There are surely other good ways.

The most simple settling tank I've seen was a cement hole in the ground next to a gorgeous cement koi pond, with the two connected by a 4-inch pvc pipe buried between them. The guy drew from the settling tank with his pump right beside it and pushed water to a huge waterfall, and he could vaccuum out his tank real easy any time he wanted.

Most people make their settling tanks ponds instead, with plants and frogs, etc., and cleaning them out is more of a chore, but they're pretty in the meantime.

The description that zinniachick gave is exactly how mine works. I have a 3 in line coming from a bottom drain that flows in to SP. From there it gravity flows to two 55 gal filters . At this point I use a 750 sequence to pump to a 100 gal skippy waterfall. I have a check valve between main pond and settlement pond also one going to filters. about every week i close these and open the one to drain in SP. Drain all water and junk out of SP to drainage ditch. If you look closely at the picture you can see the 3 in pipe in bottom of SP coming from BD.The check valves are beneath the 5 gal pails buried on left and right side of pond. I put a lilly in for the frogs. If you have the money . space , and time I would strongly urge a BD and SP it makes maintence on pond much easier.
[IMG]http://img.photobucket.com/albums/v638/705454/8-24-07pond010.jpg[/IMG]

Sorry here is the photo. Hope you enjoy.
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Thank you both.
I am still unclear as to how one feeds into the next. I understand the concept.
1. Does the bd pipe just 90 into the settling tank?
2. How does the 2 inch pipe that goes to the pump sit in the tank, just over the top and 90 to the bottom?
3. Is there another reason to use one besides to try to save the small ones?
4. Do you cover the 2 inch pipe with some kind of drain cover to keep the fish from be sucked into the filter?

not the best but at least has pictures:
http://www.happykoi.co.za/1.%20all%20about%20koi%20and%20koi%20keeping/how_to_build_a_koi_pond_part_4_settlement_chambers.htm

1) The bottom drain could be buried, going in a straight line from your big pond to your settling tank/pond, but it would involve cutting your liner.

Mine comes straight up the side of the big pond (a former swimming pool surrounded by a cement deck I was not willing to jackhammer), then 90 degree bend to go across the deck, then a 45 degree bend to swoop down into the settling pond in the garden behind the pool/pond. I have a little bridge that goes over the pipe so people don't trip on it.

2) The 2-inch pipe that draws from the settling pond just drapes over the side of it and ends in that box full of filter brushes I described above. I could disguise the pipe better. Maybe next year.

You don't want the pipe from the pump all the way to the bottom; you want it about mid-level in the settling pond/tank. If it sucks from the bottom it will suck up debris that has settled out. For this same reason, the inlet pipe that blows water from the big pond to the settling pond is usually low, almost to the bottom, (not quite) and sometimes has a bend in it to help the water swirl and settle out debris.

3) Settling ponds seem to keep the big pond cleaner. This is year four for our pond, and it is the first year it has been clear all summer. Maybe this year it finally has matured, but this year it finally got connected to a settling pond, too. Plus my pond is all fish and no plants, so the little pond lets me have some plants in the system and a place for frogs.

4) The intake basket with brushes in it before the pump keeps most living things from going through the pump.

I might try for some photos tomorrow, but it's a mess out there right now.

Very informative, but I am afraid I just got myself more confused!

Do all set ups need this settlement tank? What if they cannot be gravity driven? I thought the idea of the pressurized filter system was that the pump could be behind the filter(wouldnt that be smart?)

Just when I thought I had this all thought out....

Thanks for any help

jd....

I used a 55 gal barrel as an SC, as shown in this picture. I have a microscreen filter that is NOT shown in this picture. The elbow at the 4 o'clock position is from the BD and skimmer, gravity fed. Gate valves allow for throttling the flow from BD & skimmer, or for instance I shutoff the skimmer to clean it. This inlet into th ebarrel is about 1/3 up from the bottom of barrel.
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The CENTER pipe is suction out to the pump, you can see this pipe exit at about 10 o'clock. This pump suction line is visible rising out of the dirt if you follow out the 10 o'clock path.

The pipe at the outside edge is the DRAIN from the bottom, later cut off short - slightly below grade, now has an elbow, horizontal extension and gate valve to allow draining gunk. This 2', wish I would have made it 3' size so leaves would not hesistate as they do w/ 2' line.

another excellent picture and description here:

http://www.catson4ponds.com/VortexFilter.html

Here is a link that might be useful: vortex