[Meta menardi]

First of all, welcome to the site. I think that every pond will find it's own equilibrium, imagine some beautiful dragonflies in the garden and your pond finding it's own ecological level. There are some very interesting bits in Konrad Lorenz's book, "King Solomons Ring". He was a pioneer of the study of animal behaviour, and describes trying to maintain un-natural habitats and how they go wrong. Don't fight it, go with it.