I get questions about this constantly, so thought it would be a good time to repeat the laws of pondkeeping. Follow these tips and you will have few, if any, pond problems:
First of all, you need to realize that a pond is a living breathing organism that needs little maintenance if it is started properly. If you obey the following 10 laws, your pond will be happy and healthy and in turn, make you the same.
1. You must have one bunch of anacharis (underwater grass) per square foot of water surface area. This serves as a natural filter and as food for the fish. It grows faster than the fish can eat it.
2. 50 - 60% of the surface of the water must be shaded with floating plants. Water lilies are great, as are water hyacinths, water lettuce or water poppies.
3. You must have fish to complete the balanced ecosystem. I recommend common goldfish. Do not put Japanese Koi in your pond. They will eat all of your plants...and they will do it quickly. If you have a koi pond, you have an outdoor aquarium and must treat it as such.
4. Do not feed your goldfish. EVER!! They will become too big for the pond and upset the ecosystem. You will have an overpopulation problem and eventually all of your fish will die. You may break this law, but if you do, you must have filtration in place.
5. Put in one linear foot of fish for each 25 square foot of pond surface area. If you have 100 square feet of pond, you may have 4 foot long fish, 8 six inch fish or 16 three inch fish and so on.
6. Do not allow turtles, crawfish, alligators, ducks, geese, dogs, raccoons or possums to swim in your pond.
7. Do not use chemicals!!! EVER! Add a dechlorinator when you first fill the pond and then when you add more than 10% water afterwards.
8. Do not worry about pH. It will take care of itself.
9. Remove any dead or decaying vegetation regularly so that ammonia does not build up and foul your pond.
10. Relax. Your pond will generally take care of itself. I recommend benevolent neglect as the best approach to pondkeeping.