I'm not sure it's all that hard, or at least I didn't
work all that hard at it...
I set up a shallow water pond. Filled it full of
plants and let it go. The only outside influence
it had was being hit by the sprinklers at night
and I added water from time to time when it
got really hot out. (Live in an arid area with hot
summers.) It was full of plants, snails,
aquatic insect larvae and frogs/tadpoles. It had
fish for a time, never fed, but I decided they
would eat too many frogs eggs and I really wanted
a lot of tadpoles/frogs so I took them out.
The only way it got out of balance was actually
Mother Nature's plan - the plants started filling it
in and I decided not to invest a lot of labor to weeding.

My other pond has fish and plants and the fish are not
fed. It does have a waterfall. The fish waste is taken
care of by the plants, including a heavy growth of
hornwort and the waterfall full of rock. Everyone
thrives and reproduces. I suspect there are insect
larvae in the hornwort. Snails get eaten and I haven't
seen any outside the waterfall container.

I like fishless ponds best of all as you get more
opportunities to see more critters. I have a deck
pond that has seed shrimp and tubiflex worms in
it, in addition to snails and tadpoles.

k :-)
http://tinyurl.com/6bguh ~ new pond keeper info
http://tinyurl.com/yp64db ~ slide show of pond