I have a 100 gallon preformed pond built into a crumbling rock wall. Honestly it was made mostly for the plants- its a jungle of umbrella palm, imperial taro, Hardy water lilies (1000 petals-white, and Sioux-changeable), globeflower, monkeyflower, lizardstail, miniature cattail, azolla, anacharis, cardinalplant, water clover, water hyacinth, sweetflag and duckweed. We divide the plants every spring, and give away lots of plant babies. Since the pond is so small we can't overwinter fish, so we just get 3 baby koi or comets in the spring, and give them away at the end of the season (considerably larger). We don't use a regular filter beacuse the plants do most of the work, it's run by a simple pump with sponge prefilter and bell fountain, and we do regular water changes. Also, the wildlife loves it! Frogs and toads breed regularly in it, dragonflies have appeared from nowhere, and we make sure to not add any chemicals other than water conditioner due to the fact that birds, chipmunks, squirrels, and even the neighbors cat like to drink from it. If we had a bigger yard we would definitely have a bigger pond, as it has been extremely rewarding since we built it.
