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

By Lee Parker

No one likes to see the surface of their finned friend's habitat covered in an unsightly film, especially if the cause of the gunk is unknown. Film on the top of a betta's tank could be due to protein residue in the water, a colony of bacteria invading the tank or high romantic hopes on the part of your betta. Fortunately, there are ways to eliminate or manage all three sources.

Protein Potential

Is the film:

  • Gray or white?
  • Sludgy?
  • Re-occurring even after a water change?
  • In a tank that has little to no surface agitation?

If so, you've got a nasty case of protein film. Protein films are relatively harmless, although if left undisturbed they can trap gasses and toxins in your tank. More importantly, you should determine its exact cause to eliminate repeat formation.

A common trigger for protein film formation is the natural release of fats and proteins from feeding live or frozen food, such as bloodworms or brine shrimp. This is more likely to occur when you overfeed your betta, and leftover food decomposes in the tank. To prevent overfeeding, feed your betta on a consistent schedule, and no more than he can completely consume within three to five minutes, once a day.

Bacterial Bonanza

Is the film:

  • Rainbow-colored or oily?
  • Also on plants, rocks or objects in the tank?
  • Emitting an unusual odor?
  • Foamy or cloudy?

If you answered yes to any of these, you've most likely got bacterial biofilm in your tank. Biofilm is a common nuisance in aquariums and natural stagnant environments, but fortunately it is easily treated. You will need to fully change the water and sanitize the entire tank to eliminate the bacteria. Infections that are left to linger can make fish in the tank extremely ill, and are potentially lethal.

You can sanitize the glass portion of your betta's habitat by soaking it and all plastic implements -- including the net you used to remove your betta to safe, temporary housing -- in a solution of 1 part bleach to 20 parts water. Do not sanitize rocks and gravel in the bleach, however. They are absorbent and will later release fatal toxins into the water of the tank. Instead, fully replace the substrate, or heat it in an oven at 450 degrees Fahrenheit for at least an hour. Let the rocks cool before putting them back in the tank.

Double Duty

Another aid in the fight against both protein film and biofilm is to install something that agitates the water. Now, some betta have long and flowing fins; a tough, motor-powered filter is probably not the way to go. Instead, consider an air stone, or a spray current for larger tanks. These both constantly disrupt the surface of the water, supplying your fish with more oxygen, releasing harmful gasses and preventing films from forming.

It is always best to confirm with your vet or a local aquatic specialist if you have repeat issues such as films, or if your betta is also acting lethargic, has discolored scales or fins or is not eating. These films, while typically benign, can quickly lead to negative consequences if left untreated. They can also sometimes be indicative of a much bigger problem in the tank.

Bubbly Betta

Is the film:

  • Composed of tiny bubbles?
  • Gathered mostly on the rim of the tank, or clustered underneath plants?
  • Found in the tank of a male betta?
  • Seeming to appear in new spots on a daily or weekly basis?

If you've answered in the affirmative to any of these, congratulations! You are the proud owner of a happy and healthy betta -- a betta that's been busy building "bubble nests." Male bettas that are content in their habitats will attempt to prep these nests for eventual young, even if there are no woo-able female fish around.

Not all male bettas will build bubble nests -- even happy ones -- but the appearance of one in the tank is a good sign. If these little clouds of bubbles mar the aesthetic of your aquarium, you may simply skim the nests away, or employ a filter to keep a continuous current in your tank: Strong movement in the water often discourages romantic nesting notions in even the happiest of bettas.