Oxygen plays a vital role in maintaining a healthy pond environment. Fish need oxygen to breathe and oxygen-rich water allows efficient biological filtration. A stable pond environment with clean and clear water depends on oxygen.

Testing is the most accurate way to determine if there is enough oxygen in your pond. However, there are several cues that can alert you of low oxygen content in your pond. Pay attention to the following signs for early detection and timely correction of potential problems.

• Fish gasping at the surface - Fish gulping near the surface, at the entry of a water stream, or near other water features are likely oxygen starved. Pond fish such as Goldfish and Koi thrive in oxygen-rich waters and are not tolerant of low oxygen levels.
• Foul odors - In poorly oxygenated ponds, decaying vegetation, excess fish waste, and other organic matter can emit distinct smells. A strong "lake" smell may indicate poor water circulation, filtration, or aeration.
• Aggressive algae growth - A thick layer of filamentous or string algae suggests excess algal nutrients, including carbon dioxide in the water. Ponds without active aeration or gas exchange provide ideal growing conditions for nuisance algae.

To avoid unnecessary stress on your fish, incorporate oxygen tests as part of regular routine maintenance. In addition to the oxygen test, use the PondCare Pond Master Liquid Test Kit to measure and monitor essential pond water parameters. Since pond water parameters including pH are affected by oxygen, routine testing provides a comprehensive overview of the health of your pond.

The easiest way to improve the oxygen content in a pond is to increase water movement or to add an aeration device. When water tumbles vigorously over rocky streams and waterfalls, it comes into greater contact with air. Harmful gasses are released, and oxygen is incorporated into the water. Pond aeration devices such as water fountains, bubblers, and spitters break the water surface to encourage gas exchange. Air pumps inject air directly into the water to oxygenate ponds throughout the year.

• Remove waste - Decaying matter uses up oxygen. Use a net or vacuum to remove leaves and settled debris from the bottom of your pond. Simplify this task by skimming surface debris before it sinks.
• Provide shade - Floating water plants are a fast and easy way to provide shade. Water that is cool in temperature is able to hold onto more oxygen than warm water.
• Plant the right plants - Add a mixture of pond plants, including marginal plants, floating plants, and submerged plants to help decrease algae growth. Oxygenating plants such as Cabomba help increase the oxygen level and improve water quality.
• Maintain proper filtration - Clean pond filters regularly, especially before leaving on vacation. A clean filter works more efficiently to provide vital water movement and waste-removing filtration.
• Adjust oxygen levels to match fish population - Fish are a joy in the pond, but keep in mind that a heavily populated pond will require more oxygen. If your bio-load is high, hobbyists should make sure there are enough aeration devices to maintain proper oxygen levels.
• Fresh, clean water - A partial water change, no more than one-third at a time, can replenish oxygen and improve water quality. Remember to use a chlorine neutralizer if you have municipal tap water that contains chlorine or chloramine.