I was surprised to see no posts here already ? Anyway, I have two small ponds (more of outside raised fishtanks really), both made from railway sleepers and liner. The smaller one is 162 gallons and is on the patio. Filtering is by a Titan 200 solids pump and a Bioforce 2200UV pressurised filter with UV. This is completely raised and is only 2' deep, with Parrots' Feather, some Water Lettuce and a mini version of Alba (white) flowering water lilly. The inhabitants are two Sarassa Comets and 7 small goldfish that we raised from eggs when tried to overwinter some plants from..... The slightly bigger pond which is dug into the ground but also as a raised sleeper level. This is 304 gallons, with canna, two water lillys, Marsh Marigold, Lesser Spearwort, Water Lettuce, Water Hyacynth, Brooklime, Club Grass, varigated reeds etc. The filtering is also by Hozelock but a bit bigger (Titan 3000, and Bioforce 4500UV) to let me keep more fish than I should, which include about 5 Tench, 4 Shubs, 2 Comets, and I think we may have fry this year.