Fountain/filter project

[Jennie Beth]

Hi all,
I am making a basic urn fountain to go in my little pond. I can't have a waterfall so I will use my fountain for aeration and splashy noise. Short version: Big pot, pipe from pump goes up into pot to about an inch from the top. Water bubbles out over the sides and splashes into the pond.

Here's the question: If I were to fill the urn with lava rock, covered with a layer of 'pretty' rock, would there be enough circulation to act as a biological filter? I am concerned that with the water coming out near the top of the pot, there will be little or no circulation down in the bottom. What if I drilled holes along the upright pipe inside the urn? It would lower the flow rate a little, but I am running an 1800 gph pump, and the pot is maybe a foot high and wide, max. (I need to keep the top of the pipe near the surface for maximum aeration/splash, so lowering it to the bottom won't work, I don't think).

I have another filter with lava rock that will go down in the pond, but why waste the space and running water if I can add some more filtration in the fountain? It would need rocks for aesthetics anyway, so they might as well do some work, too.

Any guesses?
Thanks,
Jen

[ohbly]

You could pump the water into two pipes with valves to control the flow.
One pipe can go to the top of the urn and provide the bubbling and splashing, and the other can feed water into the bottom so that water passes up through all the gravel to make it act as an efficient filter.
You could just put a hole in the pipe near the bottom of the urn too, but it would be harder to judge the flow rates between the top and bottom.
Also you could put some kind of stiff screen to make a space at the bottom of the urn so it doesn't get silteded up, and to make it easier to backwash.

One last think- lava rock is not very good for pond filters because it traps silt and is difficult to clean.
It does work but plain gravel is better (but heavier).