The following are important bits of information which have been proven to be beneficial in pond design.
Sides: In an effort to keep predators from snatching or eating our pond fish, it is best to keep the sides close to vertical. Shelves may offer a place to put plants and lilies, yet also offer the fish eating varmints a place to stand and wait.
Skimmer: Much like a the skimmer in a swimming pool, the skimmer draws in surface debris. This helps keep dirt and leaves from reaching the bottom of the pond. Another benefit for cold climate ponds would be draw most all the water to the pump during the coldest months. This leaves the warmer water at the bottom for the fish.
Bottom Drains: The purpose of bottom drains are not to drain the pond. They are designed to be a source and location in which to draw the water from and send to the ponds filtration system. Since they are at the bottom, they also draw water from the surface and with it, the much needed oxygen. This increases the oxygen levels close to the bottom and promote beneficial bacteria and fish to thrive.
Below Surface Returns: One or two pump or filter return lines that are about 12 to 18 inches below surface offer many benefits. By turning a valve to direct flow to the below surface return, a current can be used to round up leaves sitting on the bottom and move them closer to the center drains for pickup, it can help circulate the pond when chemicals are added, it can offer exercise to the fish since Koi are a river fish and love to swim when the water temps are up. The return lines can also be used in colder climates during winter months when not wanting to use the waterfall. Be sure to add a diffuser to the output so the water does not create a current during the coldest months. The fish need to conserve energy in the winter.
Jets: Moving water promotes many benefits for ponds. They can be located to improve surface circulation from corners to move trapped leaves and crud to the skimmer. Some designs offer air educators inject oxygen.
Bottom Surface: The bottom of the pond should be kept as clean as possible. No rocks, gravel, piles of leaves or fish waste either. Rocks sitting on the bottom trap dirt and fish waste. This later turns toxic and releases a sulfide gas that can kill the fish.
Cold Months: Most people wonder if running the bio filter during the winter is needed. It largely depends on your climate. Once your water drops below 42°F, most bacteria are in a dormant like state. When the water is 42°F, fish are not eating and fish released ammonia is at a minimum. Since cold water holds more oxygen, the need for moving water is not needed unless you are wanting to keep moving water going through your pipes to minimize the chances of pipes cracking from freezing temps. One other benifit for keeping the water pumping through the bio filter is that early spring bio filter startup of benificial bacteria is quicker. This is important since the harmful bacteria are known to start growing in water temps around 44°F which is sooner then the benificial bacteria that starts up around 47°F.
U.V. Light: A UV (Ultra-Violet) sterilizer will kill the water bourn (the algae that is suspended in the water, not attached to the pond walls or waterfalls) algae cell (the DNA) as it passes through the U.V. Light chamber over the light. The dead algae are either mechanically trapped and collected in your bio filter filtration media to be cleaned from or it may settle to the ponds bottom for beneficial bacteria to consume. Another great benefit from a UV Sterilizer is that it kills parasites as well!
Water turn over rates: This refers to the number of times your total ponds water volume will pass through the filtration system in a given amount of time. This benefits the ponds water quality and the fish! The smaller the pond, the more often the total amount of water in the pond should pass through the filter. The following are guide lines only and are not held as a fact since many conditions should be considered when figuring, such as climate, oxygen levels, type of bio filter, size of bio filter, sun exposure periods, plant and fish load. If your pond is 0-2,000 gallons; The total gallons of your pond water should pass through the filter once per hour. 2,000 - 4,000 gallons; Once every 1.5 hours. 4,000 - 6,000 gallons; Once every 2 hours. 6,000 - 10,000 gallons, Once every 2.5 hours. 10,000 - 15,000 gallons; Once every 3 hours. When possible, more often is always better then less often. The more often the total gallons are ran through the filter, the environment is improved for the fish. It's like as if they were in a larger volume pond.