Selecting an Aeration System for Your Freshwater Aquarium

We all breathe oxygen – even fish. Humans inhale air, and the oxygen in the air is transferred to the red blood cells in the lungs. Fish take in water, and the oxygen in the water is transferred to the blood when it passes through the gills. Aeration is the process by which oxygen is transferred from the air to the water. This is relatively easy to accomplish in a freshwater tank, a bit more difficult in a saltwater aquarium

In your fish tank, this happens in a few ways.

  • First, on the surface of the water in the tank, dissolved gases are released into the air and exchanged for oxygen. The greater the surface area, the greater the amount of oxygen taken in, which is why fancy narrow tanks or fish bowls with very little surface area can only support a couple of fish.
  • Second, when water passes through a power filter and is exposed to the air before it's pumped back into the tank (which is the case with most power filters) the water is being aerated.
  • Finally, an air pump connected to a bubbler in the tank – an airstone or one of those little bubbling divers – provides air from the bubbles as they burst in the tank. These are all methods of mechanical aeration. Aeration also occurs when live plants release oxygen as they grow.

    Since small freshwater tanks – 10 gallons and less – have little surface area, adding aeration through an airstone can be helpful. In larger freshwater tanks outfitted with power filters, the movement of the water caused by the filter will usually provide enough oxygenated water without an airstone, although the stream of bubbles from the stone can be pleasant to watch and certainly won't be doing any harm.

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