"Steve Shapson" wrote in message
...
I have a 25'x25'x24" pond with a 60'x2' stream. 40% covered in plants. 4-6
6 inch goldfish, and some baby goldfish, a few frogs. External self priming
pump and no skimmer or biological filter. No stones on the bottom of the
large pond. The water recirculates up to a 3'x3'x12" pool with stone in it.
The water then cascades over a 36" fall into the stream. The pond is
relatively clear.

1. Do I need to install an expensive man made biological filter? If so,
can I use small stones in the smaller pond to act as surface area for
bacteria?

To answer the first question, no. To answer the second question, you've already
got a biological filter with stone in the smaller pond, and the plants in the
main pond. Your water is clear. You fish, I take it are healthy, as are your
other aquatics. If it ain't broke... Which answers the first question as well.

2. Do I need to clean the bottom of the main pond on a yearly basis?

A lot of people do find that they have to do this on a periodic basis.
Eventually, we all do. I use aquazyme to help reduce the amount of sludge build
up in my pond, It works pretty well. My pond has been set up for over two
years, and I've not had to clean the bottom or the main filter out yet.

If so, why? Can I do damage to the natural system by stirring it all up?

Usually a bottom clean involves either using a suction system (like a shop vac,
or pool vac) to suck up the sludge, or else you can drain the entire pond and
clean it out (which usually involves a nearly complete start over). Disturbing
the pond in such a manner will inevidibly disturb the natural system, but the
alternative is a continuous supply of unwanted nutrients feeding a potentially
worsening algae monster. In addition, sludge build up in your pond can produce
hydrogen sulfide, which can kill the animals in your pond, and can even make you
sick if you breathe enough of it. Nor does it smell very good.

3. Evaporation? Given the dimensions above and our summer temps in the
60's to 70's, I have noticed that the level of the large pond area has a
loss of about 1/8" for two days. We've had no rain. Given the surface area
of my larger pond area and the length and width of the stream, is there any
evaporation that I could actually measure?

You've already measured it. It's 1/16"/day, or 1/8"/two days, that is, if you
have no leaks.