Backyard ponds are, by and large, artificial constructions with an ecosystem that demands constant support. It’s probably not realistic to expect a pond to adequately manage its own debris and waste to the point of crystal clear water without the aid of a filter, good design, and a carefully balanced population of plants and fish. If you simply want a pond that doesn’t have dark green-tinged water from an overgrowth of algae, however, you definitely have some options.
Green water is caused by the presence of single celled algae that floats about freely and doesn’t attach. Its growth is fueled by plentiful nutrients in the water, abundant direct sunshine, and an absence of competition. Accordingly, your job is to remove these fuels. Aquatic plants are an important part of your arsenal because they compete for the same nutrients as the algae (nitrates, phosphate, etc.). Plants (whether aquatic or border) also provide shade, which reduces the availability of direct sunlight. Surprisingly, a good stealth approach for taking out algae is the deployment of a completely different kind of algae - diatoms or brown algae. These little heroes compete with green algae for the same nutrients, but instead of removing oxygen from the water, they actually add it. Improved oxygenation is great for your fish and prevents the growth of toxin-producing and odor-causing anaerobic bacteria. Aside from directly addressing problems with algae growth, you’ll need to actively manage the sludge/mulm/detritus at the bottom of your pond. Not only does it add excess nutrients to your water as it decays, it produces huge brownish clouds when it’s disturbed by active fish or even turtles and other wild visitors. Finally, if you’re operating a backyard pond, especially one that includes fish, it’s important to monitor your water chemistry regularly so that you can catch imbalances early rather than waiting for visible signals of a developing crisis.
