We bought our first house last fall, and it came with a 1500-gallon pond (which had a lot to do with our decision, incidentally, as I'm a HUGE pond fan). In any case, I've had aquariums of varying sizes but never anything of this scale. Here's the setup:

-1500 gallon pond with two drains on the bottom and one overflow drain at the top in case of heavy rain

-Water goes from one of the two drains (there is a switch to pick which one) into an underground pre-pump filter basket, then through the pump into 2 approx. 100-gallon open-top barrels

-Both of them have biological filter material (bottle-cleaner looking things hanging down from the top) and drains on the bottom

-After the water goes through the two tubs it goes into a waterfall and back into the pond.

Seems to be pretty self-sufficient, I only drain out the tubs and clean out the pre-pump basket every month or so and the water is very clear. However, when I drain out the tubs the water that comes out is kind of smelly and I see little tiny critters crawling around in the tubs. Is this normal?

And is that smelly water good for plants? :-)