Healthy Fishpond With No Filter?

[Mehitabel]

Hi All.
I'm fairly new to pond-keeping. One thing I've believed right from the start is that if you're going to keep fish in your pond, you MUST have a filter of some kind. I have a 750L pond with about 15 small goldfish and a good stock of vegetation. But whenever the filter packs up, I panic, believing it'll only be a matter of days before the fish start to suffer.
But............ I have a friend with a very well-established pond, about twice the size of mine, with a lot of large goldfish. It's crammed with vegetation - don't know how the fish can move. But what really baffles me is that he doesn't have a filter, just two solar oxygenators. This being the UK, they don't do a lot of work. The pond is never cleaned or cleared, nor is the water changed.
So: Have I been misled? Am I worrying unnecessarily when my filter system throws a fit? Can you really have a healthy fishpond without one?
[Pics are of my friend's pond]

 

[Mmathis]

There are 3 types of filtration: mechanical, biological, and chemical. All are important, but it depends on what you have in your pond. If you have plants, a low fish load, and some type of water movement (through a pump, bubbles, or waterfall), it’s possible to get by without a filter. The secret is keeping all of this in balance. If your fish are healthy, the rest is all up to you. A common misconception is that clear water equals healthy water. It doesn’t. Your water can be crystal clear…..and still not be healthy. You can have algae and maybe not be able to see the bottom of your pond…..but still have good water quality. You want healthy, balanced water, that doesn’t go through drastic changes.

This is a simplified representation, but in no way implying that THIS is what you need — just an example of what each type of filtration means. There are many types of mechanical filtration. Your biological filtration is all about the biofilm of beneficial bacteria that collects on pond surfaces — it doesn’t have to be incorporated into a filter. To me, chemical is more about correcting what the mechanical and biological can’t keep up with (for example pH, KH, GH).

A good liquid test kit (not strips, which are less reliable) is always your friend if you have questions about water quality.