My father has had an outdoor pond now for about 4 years. I'm not sure on the gallons, about 500-100. It has two sections, one upper, one lower. The lower section houses the few goldfish we have, as well as a few apple snails(one is already the size of a tennis ball) and wild frogs and their tadpoles. Well water is used. Their is no filter, but occasionally the pump is run to flush out the pond a few times a week. I've argued with my dad about this repeatedly, but not much anymore. There are lily pads, anacharis plants in the pond, and algea on the sides of the liner(soon all to be consumed by the apple snails). There is substrate, numerous rocks and some sand. The goldfish look sickly to me. Most of them have ulcers on them, only one or two don't have them. I've given up arguing with my father about these issues, but I still feel I should do something for these poor fish. Any DIY solutions for a filtration/pump system and cost would be appreciated. I love every animal, even insects, and to be in a position such as this has been bothering me for a while. Ahh, the rigors of being 21, unemployed, and still living at home...