I have put in two ponds by hand, the latest at my home Im in now. I have done much research and know a thing or two about it. First thing is do NOT use a pre formed pond liner. They are too difficult to fit with a hole, they can crack and leak after a few years, and they are not deep enough for a normal st louis winter. Best way to plan it is use spray paint and outline the pond on the ground. Make sure you take into account run off from rain, gutters (roof runoff can poisen a pond over time) and where the water will go when it overfills. You dont want the low side next to the house!!
The best way for filtration IMO is a skimmer box set into the ground with the pump set down inside it. It needs to have a large holed filter bag for leaves and a smaller filter for other junk. The pump will push the water back up hill to your inflow box/waterfall, hence creating a nice flow to the pond. You will also want to get fieldstone (small flat rocks) to stack inside of the pond to give it a natural look and protect the liner from UV
Mine is 24 ft by 12 ft in a kidney shape and a bridge over it. Dug by hand ( that was a *****) but I was able to put a ledge inside the pond on which to set plants. You need to make sure it is 36" deep so the fish can stay in it year round. Some of my fish are almost a foot long and they are three years old
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