If you're serious about adding fish to your pond, you're going to need more than a pump. You're going to need a filter. That’s because fish give off by-products (hey, all that fish food has to go somewhere!). As these by-products decompose, they release into the water various waste products such as ammonia and nitrites that can be deadly to fish.

A good filtration system--whether manufactured or natural--can help prevent the buildup of chemical toxins by removing waste products, along with uneaten food, plant debris, and anything else subject to decomposition, before it has a chance to do any serious harm.

There are exceptions to the necessity of using a commercially manufactured pond filter. If your pond will contain only a few fish and lots of live plants, you can probably get by without any additional filtration, since the plants act as living filters, taking in nutrients during the decomposition process and giving off life-sustaining oxygen in return.

But, in order for this natural type of filtration system to be effective, you’ll need a lot more plants than fish, and maintaining the proper balance can become a daunting task--one of the main reasons most pond owners opt for manufactured filters.

Getting the Green Out

Algae and algal blooms thrive in full sunlight and can quickly overwhelm and clog the best of filters. In addition to looking bad (lending water that greenish, stagnant, sewer-water look), algae robs the water of oxygen, thus creating even more problems, especially for fish ponds. By shading your pond for at least part of the day, you’ll have fewer problems with algae overall and enjoy generally healthier water. You’ll also find the need to clean your filters less often.

But providing shade for your pond can be a problem, too. If you use trees—the obvious choice for shade—you’re going to have to face additional maintenance. Deciduous trees, those that go bare during winter, drop their leaves once a year. When they do, you can virtually bet that every last one of them is going to end up in your pond. You’ll need to remove the fallen debris regularly before it decomposes in order to prevent the buildup of toxic nitrites and ammonia.

Flowering deciduous trees are even worse, since the flower blossoms fall off in spring; and the leaves, in fall, providing the harried pond keeper with a continuous mess.

The obvious solution might appear to be to build your pond beneath a pine tree, which remains evergreen all year long. That's not necessarily true, since pine trees shed a good number of their needles throughout the year, as witnessed by the “pine straw” matting that mounds up below evergreen trees. One good wind or rain storm, and you’ll quickly see how much of a nuisance those “evergreen needles” can be.

Fortunately, there are some evergreen and semi-evergreen trees that are fairly clean alternatives to pines. These include Nandina, cypress, and eucalyptus trees, which may or may not be suitable to your climate. These plants rarely drop leaves, don’t have needles, and don’t flower. For other possibilities suitable to your climate, check with your local nursery or state horticulturist.

If planting trees and shrubs for shade is out of the question, consider stocking your pond with floating plants such as water lettuce and water hyacinth. For more drama, inter-plant a few water lilies and lotus, both of which produce beautiful and colorful blossoms. The plants will help to absorb Old Sol’s rays while helping to keep the water clean and well oxygenated. For greatest effect, cover at least 40 - 50 percent of the pond surface with plants.