I am building an external gravity filter (that is what I call it, not sure of the technical term)

Here is my idea. A 25 gallon Rubbermaid plastic tote. Water enters from the top and exit from the bottom back to the pond. I am using 1.25 inch pvc pipe in the tote. The tote will be filled with small river rock (2 to 4 inch size) at the bottom. These small river rocks will surround a pvc pipe with holes drilled in it. I am doing this so that the pvc pipe will not be clogged.

Above the river rocks/stones, I will place washed pea gravel. And above that I plan to place a layer of sand to create a large surface area for bacteria to grow. I read that having bacteria will be a good thing for filtering.

So to summerize. Top layer sand, second layer pea gravel(largest amount), followed by larger river rocks/stones before the water exit back to the pond.

Any feedback will be welcomed. By the way, I don't plan to have many fish. Enough small fish to keep the mosquito larve in check. The pond size will be approximately 12 by 10.

Thank you all again in advance.

AGE

Not worried if the fish multiply. I am actually going to get the small silver looking fish (bait fish) from the local river. I plan to return the fish back to the river before fall.

http://www.skippysstuff.com/biofiltr.htm

I am also thinking of building a pond gravity filter waterfall as well.. There are some good ideas on you tube

http://www.youtube.com/watch?v=NgZWOXOonZo

everyone these days like the green scrub pad as media.
You are going down the right path though I would skip out on the sand you will be fighting it cloging all the time

let me know what you decide to do? Mine will only be 4 x 7 or so I think

I could not find cheap filter media online. Every place wants an arm and a leg for filters. Do you know any place that is cheap?

Good luck on your filter also hhiii.

River rock tends to be heavy, though, and one must plan ahead how to clean the filter without removing the media. Up-flow designs are preferable so that heavy crud can be drained from the bottom. I designed mine to drain through the inflow manifold and once a year this filter is drained to the bottom.

Many love the skippy filters, and I can't argue with them. If it were me doing a 10 by 12' pond I'd be thinking rather larger than 25 gallons. I'd be looking for at least a 100 gallon stock tank or considering doing one with rubber liner larger still. If you fill it with gravel the liner plan becomes pretty easy to make and to finish next to an in-ground pond. Bigger problems, though, figuring how to drain (backflush) it. A sump pump at the bottom does that trick for some folks; mine just goes by gravity into a nearby pump pit.