My friend with big pond and really huge koi (she used to sell fancy GF and koi) had
two big hunker Big Sister filters. Despite that her husband had to do these big
water changes every week (koi were his). Then she needed an eye operation at the
same time her husband had knee replacement and she came to the sudden realization
that the ammonia had almost gone off chart, one koi died and the others were breaking
out in sores all over. She literally had the water running all day into the pond (her
own well) and it just wasnt bringing the ammonia down very well. She was desperate.

I sent her one BIG clump of water celery. She put that into a kiddy pool she had
rigged up in front of the output of one of the big sisters. In 10 days there was no
ammonia. And they dont need to change water.

Any other filter in the world will convert ammonia to nitrate, and nitrate is toxic
above 20 ppm and there are no aerobic bacteria that remove nitrates. So water
changes are inevitable.

OTOH, veggies will take the ammonia right out of the water and use it completely.
"About a year ago there was an article by Diana Walstad that said something
to the effect that aquatic plants preferred ammonium over nitrate.
She based her article on a peer-reviewed publication that cited
results from a study done with Spirodela (a kind of large duckweed).
This floating plant was grown in a mix of equal concentrations of
ammonium, nitrite and nitrate. Tests showed that the ammonium was
absorbed first, and nitrate last. Nitrate *was* used up, but only
after practically all the ammonium ions were gone."

Veggie filters are simply easy and can be configured to be absolutely gorgeous.
http://weloveteaching.com/mypond/changes/changes2.htm
I have yet to see a really gorgous typical filter unless something is built to
entirely encase it.
Ingrid

On Thu, 27 Mar 2008 22:11:02 EDT, "mjl" wrote:
I have a 2500 gallon pond and need a new filter. I have about 12 good sized
koi in the pond. I am thinking about getting a tetra pressurized filter