Building a pond is no small task by any measure. I recommend a lot of planning before you dig. The more you plan now the less you will wish you could change later.
The First thing to consider when you start to plan is where you will be putting it. The Pond should have both sun and shade; the plants need sun but the fish like a little shade. The roots from some plants may seek out your pond, as well as the problems with the leaves and flowers of others. Rhododendron bushes are a perfect example their leaves and flowers are toxic to fish. Leaves and dead plant matter in general will rob the oxygen out of the water as they decompose. Last, but not least, you will need a place for water and electricity as well as most importantly a comfortable place to sit and relax.
When you have decided where you want to put your pond, the next question is what it will look like. Do you want a formal pond with a geometric shape or a more natural shape that follows the lay of the land? When you do decide what you want, many recommend using a garden hose to define it's. I recommend using cheep rope, if the rope gets cut during the digging who cares. Cut your favorite hose and face the wrath of your wife. Once you have laid out the general shape of the pond I found that by putting landscape fabric or old sheets etc, in the pond area helped me see the true shape. Afterwards you can put pots, garbage can covers, etc in to plan out where you want to put plants, waterfalls, fountains, or whatever you want. Planning now can save a lot of backaches later.
Now that you have an idea of what your pond will look like, from above, lets go down below. I have found two schools of thought on pond building. The first being digging shelves in the walls of the pond. This has the advantage of easy placement of bog plants. The problems deal with erosion, do you have solid enough soil for shelves, or will you have to build cement edges for the shelves. Secondly, the shallow water of a shelf will invite visitors. Cats, raccoons, and other animals are more apt to come in for a visit if they think that they can get back out. High walls and no shelves can prevent visitors. The lack of shelves leaves you with the problem of how do you put your marginal plants in the pond. I went with deck hangers for potted plants. The vinyl-coated hangers can be submerged w/o a problem and come in many shapes and sizes. I also used cinderblocks to support my water lilies. In afterthought I wish that I had built a bog between my filter and my pond (I may yet.). A bog not only gives you a great place for marginal plants, but it also will help in biological filtration, which I will get into later.
Time to figure out the size of your pond. Chuck Rush has a wonderful pond calculator.
US Measurement Metric Conversions
OK now that you have figured out the size and number of gallons, and the fact that filing the pond will form a drought condition, let's talk filtration.
The topic of Filtration is one on which volumes have been written. There are two main purposes for filtering the water:
1. To remove floating materials - mechanical.
2. The Ammonia cycle.
Mechanical filtration is the process in which suspended particles are removed from the water. If you look around, you will find that this is usually some sort of open cell foam that can be rinsed out and reused. Often, if foam is not used, spun fibers, like pillow stuffing are used. I prefer the foam, it is easier to handle and very easy install if you build your own filter. The Ammonia cycle is also referred to as biological filtration. This is where bacteria convert Ammonia to Nitrites and Nitrites to Nitrates. This is one delicate balance that must be maintained ammonia and nitrites will KILL fish quickly. Excessive nitrates, while not hazardous to fish, excess is not a good thing. Excess nitrates will promote growth of plant life i.e. ALGAE, yuck! Seeing as how important this is, it must be very hard to accomplish, right, wrong. All you have to do is provide living space for the bacteria to grow on. I like lava rock for this, lots of surface area. Secondly, you need to put something to absorb the nitrates (plants) I like Water Hyacinth and Water Lettuce. They will both float on the top of your filter, and cover it better than any lid. If you live in the South, or are having a long hot spell, you can even get the most unique blooms I have ever seen. When you have enough, and they are overflowing, just throw them in the pond. Koi love to eat them. DO NOT let this plant out of your pond and into the local waterways. It is invasive and can cause damage to the environment by filling the area it is given with a dense cover.
However there are just a few things that you will find in all pond filters.
1. Aeration - adding Oxygen to the water by having it pass through the air or air pass through it.
2. Mechanical - A series of materials designed to catch suspended debris in the water
3. Biological - Living space for bacteria which will convert ammonia to nitrite to nitrate.
Each of these are important and can be provided in different ways.
Aeration can be done by having an aeration tower through which the water tumbles, a waterfall which is much the same and lastly you can use a venturi jet to inject air into water. The important thing is that your fish and plants get the air they need.
Mechanical filtration can be done in a multitude of ways, but mainly you will find screens or open cell foam being used. One thing you want to remember is that occasionally you will need to clean out the filter. Make sure the filter material is accessible and that you have a place to rinse it out. (I use my garden, it is a great fertilizer.)
Lastly and most importantly is the biological filtration. This involves providing a surface on which bacteria can grow. I use lava rock, which gives you quite a bit of area per piece.
Getting the water moving to the filter is as important as the filter itself. There are many different types of pumps on the market and just as many sizes. So which one do you need? The answer is not that simple. The way they rate these pumps is in gallons per hour (GPH). How much do you need? Not everyone agrees, but I feel that you should pass your every gallon in your pond through the filter once every 2 hours. There is another problem and that is that the "head - the point where the water comes out from the pump" is not at the opening of the pump. You need to pass it through some pipe to get from the pump to the waterfall or filter. The problem is that every bend and turn reduces the flow. Another thing to consider is that if you decide to use a ribbed hose instead of tubing you will drastically reduce the flow. I learned this information a little too late when I started with my pond, I was having all kinds of trouble with green water. By changing from 3/4 in. ribbed tubing to 1-1/4 in. PVC pipe, I resolved all of my green water problems. Occasionally you may wish to do a water change / inspect your fish / move your plants around, I have found that going to your local boat shop or Boat U.S. you can get a bilge pump which works off of 12 volts. These little powerhouses will move a lot of water in a little bit of time. They also serve a dual purpose. You can vacuum the bottom of your pond with them and you can use them as an emergency pump in the event of a power failure you can always pull the battery from your car and use it to run the pump. (The fish are more important than your job, aren't they?)
What type of pond you want will help determine what you will use to manufacture your pond. The simplest of all are the prefabricated pond liners, which are found in many lawn and garden stores. This is the quickest way to build your pond, but it has many drawbacks. First all the thought about design, must be centered around what is available for you to purchase. Secondly, if you live where there are freezes, you may not be able to keep your fish in the pond all winter. In the south, you have to keep your pond cool so you don't come home to a boiled fish dinner. Lastly, pests are not afraid to go swimming after your fish if they can see the bottom is not that far down. Cement is another common material for building ponds, again there are drawbacks. The first of which is that they can crack, and then are very hard to repair. Also if the water table rises above the bottom of the pond, you could pop it out of the hole. One of the advantages, is that is you do get visited by a dog or raccoon you will not puncture your liner. Another advantage is that you are not as restricted by shape. I prefer to use Flexible liners. These liners are made of EPDM rubber. They come in different grades, but the most common are 45 mil and 60 mil thick. I have never used 60mil, but 45 mil is serious stuff. I had one of my dogs "fall" into the pond and scramble out, without cutting the sides. (Jaycee is a 70-lbs. Setter with a newfound healthy respect for our pond.) To cut the liner, you will need something very sharp. I have used shingle knives, and I found that the razorblades they sell to replace shingle knives are perfect. Do not cut it until the pond if full, a lot will be taken up in folds while it fills. When you have your hole dug, your liner purchased your pumps and filters ready, have a party. Why? The liner weighs more than a Buick and you will need those "friends" to help you lay the liner. I hope that I have provided you with some insight into building a pond. I will address fish in another section. If you have a question please e-mail me, I will answer as soon as I can. If I do not have your answer, I will direct you to a few others who may. I hope you enjoyed the info.