What Is the Film at the Top of the Betta Fish Tank?

If you look at the surface of your betta fish tank from a certain angle, you may notice a rainbow effect playing across the surface of the water. This rainbow effect indicates the presence of a film on the water. It is not uncommon for film to develop on the surface of betta tanks, particularly when there is no filter or air pump to facilitate water flow. The film itself is not dangerous, but it can affect the water quality in your betta tank, so it is best to take steps to remove the film and prevent its recurrence.

  1. What is it?

    • The term aquarium hobbyists use to describe the film that forms on the surface of aquarium water is biofilm. Biofilm is simply a thin film that forms as proteins build up on the surface of the water. This film may serve as a support structure for the bacteria that live on the surface of the water, and it may also simply be an accumulation of organic debris. A film may also form on the surface of a betta tank when the male betta builds his bubble nest in preparation for spawning. The mucus the male betta uses to hold the bubbles together can result in a film on the water surface.

    Is it Dangerous?

    • Because the film itself is likely composed of built-up proteins or mucus, it is not harmful to fish or humans. You can safely dip your finger into the water to break up the film without putting yourself or your fish at risk. A problem may arise, however, when the film starts to thicken. Over time, the film could prevent the tank water from absorbing oxygen from the air above the surface. This film could also inhibit the release of carbon dioxide from the tank water, thus causing a build-up below the surface that could be harmful to fish and the beneficial bacteria in the tank.

    Removing the Film

    • The easiest way to remove the film from the surface of your betta tank is to induce water movement. By installing an aquarium filter or air stone, you can keep the water in your betta tank from remaining still for any extended period of time. If the water in your betta tank is always moving, there will be no opportunity for proteins to settle and to form a film on the surface of the tank. A short-term solution for removing film from the tank surface is to use a mesh net to scoop up the film.

    Protein Skimmers

    • If you experience frequent problems with film forming on the surface of your betta tank, you might try installing a protein skimmer. Protein skimmers can be used in conjunction with several types of aquarium filters, and they literally skim dissolved proteins from the surface of the water to prevent build-up. Though these devices are most frequently used in saltwater tanks, they may help to prevent the formation of biofilm on the surface of a betta tank.