1. Many of the reasons for cloudy water are because the pond is built improperly. The water level in the pond must be above the surround area. If it is not, run off when it rains will go into your pond. So all the dirt from roads, grass or lawn, roofs, and driveways will end up in your pond. If you have built your pond below grade, you will need filtration to keep the water clear. That filtration can be as simple as a submerged foam rubber filter, a container of lava rocks that the pump sucks water through or as extensive as an exterior bead filter with a UV light attached. But you will need filtration or your water will always be cloudy and algae filled.
2. If you have koi, you need filtration. Koi are magnificent eating machines. And the more they eat, the more waste they produce. Fish waste feeds algae and algae turn your water green. If you want to keep koi, think about a bead filter or at least an exterior sand filter.
3. If you have goldfish and feed them, you will need filtration. Usually a lava rock homemade filter will be sufficient, but sometimes, if you have a large amount of fish in a small pond, you will need a large filter system. As with koi, go with an exterior bead filter or submerged commercial filter system. If you balance your pond ecologically and do not feed your fish, you will need no filtration at all.
4. Cover half the top of your pond with floating plants. When sun hits water, algae form. Keep the water half covered and half as much water will be in the sun. Use water lilies or water hyacinths. Water clover or water poppies work well for natural cover.
5. Watch your bioload. If you have too many fish, the fish waste will not be absorbed by your ecologically balanced pond and the water will turn green. One linear foot of fish per 25-square feet of pond surface is a good rule to follow.
6. Know the pH of your water. If it gets on the basic side, algae grow and the water turns green. Usually this will fix itself if the pond is balanced. If it doesn’t after a couple of weeks, you can buy a commercial product to lower the pH or you can use muriatic acid. Be careful if you do. It can be dangerous.
7. If you find string algae or blanketweed, a common problem introduced into ponds, usually with new plants, a bale of scotch barley works to eliminate it. Be patient. It can take as long as a month to work. Always put another bale in the water before the old one is completely decomposed.
8. If blanketweed continues to be a problem, you can use a black dye for about 3 months to be rid of the stuff for good. Black water is great in a reflecting pool and water lilies look great swaying atop the black water. Your submerged vegetation will not be harmed.
9. You can use a commercially made product and they work well for blanketweed control. Just be very careful in the application because the algae clump at the bottom and can deplete pond water oxygen. If that happens, your fish will die.
10. If you are under a tree and your water is a brownish color, the tannin from the leaves is staining the water. The only way I have found to clear tannin is to use activated charcoal in your filter. You can find it in an aquarium store. Wash it first, put it in an old panty hose leg and put it in your filter. Change it when the water begins to turn brown again. Do NOT use the charcoal you barbecue with. It is not the same thing.
Ponds are the focal point of our gardens. We want our water to be clear and clean. The best way to do that is with benevolent neglect and keeping the pond balanced ecologically. But if you wish to feed the fish or keep koi, you must work a little harder for clear water. Using these few easy fixes will do that for you.
Article from Jan Goldfield, Yahoo Contributor: http://www.associatedcontent.com/article/1427418/how_to_keep_your_pond_clear.html?cat=32