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I built this pond for my living room in two days. The total cost was less than $200, using common tools and other items available at your local hardware store or home and garden center.
Step 1Initial design
Decide where you will put your pond, and how big you want it to be. I chose to make mine 4' X 4'. The actual frame is 16" tall, but the water is only 8" deep, and raised up 8". One thing to consider is that 1 gallon of water weighs about 8 pounds.
Here is a link to a good pond calculator. My pond holds about 70 gallons (560 pounds). If you place your pond on an upper level of your house, you should try to place it along a load bearing wall. A larger pond should be placed on the ground floor. Please make sure your floor will be able to hold your pond. Nobody can be held responsible for any catastrophies but you. Do your homework.
This link is a good place to start. FYI, a waterbed holds ALOT more water than this!
How many fish in your pond and any other problems with the pond or the keeping of your fish. i e the light factor?
Carp such as koi and goldfish grow continually, releasing growth regulating hormones into the water. Once the hormones get to a certain concentration the fish stop/slow down growing. Unfortunately, by this time they are already larger than the tank can safely sustain (one 1 inch long of fish per gallon, eight gallons per 4 inch long fish, 32 gallons per 8 inch long fish, ect.-larger fish produce more waste and need more water per inch of length than smaller fish).
Interestingly, when my sister was in Japan she saw carp (unknown if they were koi or goldfish/comets) that were six FEET long. The temple pond was continually fed/flushed out by a mountain stream so the growth regulating hormones couldn't even begin to build up. Unfortunately she couldn't get any good pictures.
You can do a fishless cycle by tossing a couple frozen shrimp into the pond. As the shrimp decomposes, ammonia is released, providing a food source for the bacteria and starting the nitrogen cycle. Then just start testing the water after about a week or two.