Source of Oxygen in Salt Water

Saltwater animals need oxygen to live. In freshwater and on land, oxygen is produced by plants. Some oxygen in salt water is produced by marine plants, but most is dissolved into the water from the air.

  1. Oxygen in Water

    • Saltwater fish breathe dissolved oxygen through their gills.

      Plants breathe carbon dioxide and break it down into carbon and oxygen. They give off oxygen as waste. Almost every other organism must breathe this oxygen to live. All vertebrate and invertebrate animals and most microscopic organisms need to breathe oxygen. Some blooms in water that look like algae are actually protozoa and bacteria that need oxygen to survive. For these living things to breathe, oxygen must get into the water.

    Water Movement

    • Standing water has too little oxygen.

      Oxygen makes its way into salt water from the air by movement at the water's surface. As the water moves, molecules of oxygen become trapped and dissolve. Movement deeper in the water column distributes this dissolved oxygen. Most saltwater animals take in oxygen with their gills or skin. Blue-green and green algaes (including seaweeds) create some oxygen, but most is produced by plants on land and dissolved into the water. In a saltwater fish tank, you must provide a source of dissolved oxygen.

    Filtration

    • A filter provides oxygen in a fish tank.

      Filtration is the primary source of dissolved oxygen in a saltwater tank. There are three kinds of filtration. Biological filtration removes debris and is provided by the tiny organisms on live rock. Chemical filtration also removes debris and dissolved materials, and is provided by filter cartridges. Mechanical filtration sucks water out of one part of the tank, filters it, and puts it back. Mechanical filters can contain biological (biowheel) and chemical (charcoal) parts. Mechanical filtration moves the water and dissolves oxygen. It must always disrupt the surface of the water to provide enough oxygen. The more the surface is in motion, the more oxygen is provided.

    Aeration

    • A bubbler is rarely necessary with proper filtration.

      An aerator blows bubbles into the water, usually through a tube attached to a pump. Filtration is necessary. Aerators are not, however. The bubbles do not release very much oxygen into the water. An aerator can add some oxygen as long as the bubbles disrupts the water's surface.

    Plants

    • Plants add oxygen to water, but saltwater plants are not readily available for fish tanks. Attempting to put seaweed from a body of water into your fish tank is likely to spread disease and cause decay. Wild algae may enter your tank in saltwater or on live rock. True algae adds oxygen, and some experts recommend allowing algae to grow undisturbed at least on the far wall of a tank.

    Beware of Toxic Blooms

    • The wrong microorganisms can harm a fish tank.

      A problem arises if true algae causes a protozoa or bacterial bloom. This happens when the extra oxygen allows microorganisms to reproduce. Plants produce oxygen only during daylight, but other organisms consume oxygen day and night. During the day there is plenty of oxygen, but at night, when the extra oxygen supply is turned off, the extra microorganisms may consume all of the oxygen in the tank, suffocating fish and invertebrates. This is rarely a problem with proper filtration. True algae is usually green or bluish. Toxic blooms are usually brown or red.