There are many ways to filter the water. From a vegie filter to a tower trickle filter even home made ones. Google each one till you find something that works for you and your budget. There are many name brand filters as well, Lagoona, nexus, pondmaster ect. Look around on the web you should find something that works for you. In the meantime do partial water changes to get the numbers down.

Stardust12081,
I assume that from your numbers that the pond is about four weeks old. If there is no salt in the pond put 50 lbs in asap to protect the fish from the nitrite. I would assume that the ammonia readings are on their way down. With your current fish load you will have some time to figure out what type filtering system on the pond.
Mike

If you are even reasonably handy with tools you can also build your own. As mentioned above, trickle towers are fine (I built one out of a 50 gallon plastic pickle barrel, put in a bottom outlet, grate supported on a couple of bricks, filled with plastic media such as Bio-Fill, added a sprinkler/header to distribute the water). Some claim that they have a faster cycle rate but I haven't seen any real data to support that. Another very popular type of filter is the so-called "Skippy" filter (see URL below). I also built one of those and find it works very well. Or you can spend $$$ and buy a pre-built unit which would be delivered to your site probably on a skid which you then have to plumb and wire it up. With my New England DNA I guess I prefer to do it myself and save a few $$$ !
---David

Here is a link that might be useful: Instructions for building a Skippy