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Dissolved Oxygen

One of the most important elements of a healthy aquarium is also one of the most overlooked. Like all animals, fish and other aquarium inhabitants require oxygen to survive. Unlike air breathing animals, fish depend on dissolved oxygen in the water to “breath”. Making sure that your aquarium has proper dissolved oxygen levels is vital to the health and survival of your fish.

Many things can affect the dissolved oxygen in your aquarium. The most important things to remember are stocking levels and cleaning. Too many fish will require more oxygen than is available in the water. Fish waste, decaying food and rotting plants are all consumed by bacteria, which also require oxygen. Regular cleaning, water changes, filter maintenance and proper feeding will ensure that the bacterial demand on dissolved oxygen is under control.

There are also many things that you can do to improve dissolved oxygen in your aquarium. Most of the dissolved oxygen in your aquarium comes from the atmosphere; this is accomplished through interaction with the water surface. Increased water surface area gives your aquarium higher potential for atmospheric interaction. Turbulence and water movement along with good aquarium design will increase your aquariums water surface area, and dissolved oxygen. Use of an air pump and air stones or a power head with a venturi aeration feature will also greatly increase your dissolved oxygen. The tiny bubbles created have huge amounts of surface area and greatly increase the potential for oxygen to dissolve into the water. Temperature also plays a significant role in dissolved oxygen levels. Concentration of dissolved gas decreases with increase in temperature, so avoiding high temperatures (above 85 Fahrenheit) in very important. Taking all these factors into account when setting up an aquarium will go a long way to ensuring your long term success.

The use of ozone, especially in saltwater aquariums, can also greatly increase dissolved oxygen. Ozone is a strong oxidizer, which when properly used, will break down organic material in the water through oxidation. This greatly reduces the biological demand for oxygen, and at the same time releasing oxygen as a byproduct of the oxidation process. Ozone use is not for the beginner level aquarist and must be used safely and properly. Use of an ORP controller is highly recommended. Ozone is typically used in conjunction with a protein skimmer, or a special reaction chamber.
Until next blog,


  1. avatar

    is there any sort of chemical test or any way of monitering the percentage of dissolved oxygen in the water for scientific testing purposes?

  2. avatar
    TFP Marine Biologist

    There are both chemical test and electronic monitors for measuring disolved oxygen.
    If you look in the aquarium supplies section of our website you will find them in the test kits, and testing equipment catagories on the left hand side of the page.

    hope that answered your question


  3. avatar

    when the electric goes out.Does pouring water into the tank supply any oxygen?

  4. avatar

    Pouring water in will do very little to improve O2 levels if the tank is not running. The O2 levels should no tbe an issue immediately in a tank that is not overloaded, there will be a window os several hours until it will become a serious issue. The best solution is to have a battery operated air pump as a backup. Water changes come into play when the electric is out for an extended period, as the chemistry of the tank diminishes without filtration. If you experience an outage, be sure the tank doesn’t backflow into the sump if you have one, and monitor the fish. A battery operated air pump/airstone will help when the dissolved O2 runs low, and test the chemistry for ammonia levels to indicate when a water change may be necessary to reduce toxicity. Then hope that the electricity is restored ASAP!

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About Dave Acland

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After graduating from Coastal Carolina University with a BS in Marine Science in 1996, I started my professional career in 1997 as an aquarist at Ripley’s Aquarium in Myrtle Beach, SC. This was an amazing experience, in which I gained invaluable hands on training in exhibit design and construction, as well as husbandry skills for a wide range of animals. In 2000 I started working at That Fish Place as one of the staff Marine Biologists, with the responsibility of maintaining one of the largest retail fish holding systems in the world. I presently hold the position of Director of Aquatic Science, where I oversee the operation of our 35,000 gallon retail aquarium systems, and provide technical support for our mail-order and retail store customer service staff. As an aquatic product specialist, I also provide support for our purchasing and marketing departments, as well as contribute web content and analysis. As a Hobbyist I acquired my love of aquariums from my father who was keeping a large aquarium in early 70’s, and set up my first aquarium when I was 12 years old. I have now been keeping aquariums for over 35 years, and through this time have kept more aquariums and types of fish than I can remember. I set up my first Saltwater aquarium in 1992, which led me down the path I still follow today.