Understanding Aquarium Water Foam

Fish Swimming In Aquarium
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Have you ever noticed foam in your aquarium water and wondered where it came from? Perhaps you were concerned that it was a danger to your fish. Foam on aquarium water comes from a number of sources. Some are harmless while others can be deadly. Here are common causes of foam on aquarium water, and what can be done to eliminate it.


Bubbles form quite easily when liquids are agitated. Shake a liquid hard and enough bubbles will be created to form foam. When filling or topping off an aquarium, it's not unusual to agitate the water enough to cause at least some foam, which is normal and harmless. If you want to avoid bubbles when you fill or top off a tank, pour the water slowly against a clean plate held at an angle so that the water trickles down the plate and into the tank rather than splashing forcefully directly into the aquarium.

If you have a spray bar or powerheads, they may agitate the water sufficiently to produce some foam. Generally, this will not be in large quantities and is composed of larger bubbles that are easily dissipated. This type of foam is completely harmless and is nothing to be concerned about.


If even a small amount of soap or cleanser get into the tank, it will usually cause foam to form. This type of foam is ominous, and if your fish aren't already dead, they soon will be if you don't immediately move them to another the tank (or to a clean bucket if you have no other tank). The tank will have to be drained and everything rinsed thoroughly to remove the soap. Be sure to clean the filter as well, and replace all the filter media and pads.

One of the common ways that soap gets into an aquarium is via the cleaning materials, such as the water bucket or scrubbing pads. Make sure those items are never used for anything other than aquarium cleaning. Don't lose your fish because your aquarium bucket was borrowed to hold soapy water for washing the car. Label your aquarium buckets and educate everyone in the household about the importance of not using it for anything other than plain water.


Protein foam is far more prevalent in saltwater aquariums but is seen occasionally in freshwater aquariums as well. It is the result of protein-based waste coating small air bubbles, which causes them to stick together and form a foam. Saltwater aquariums utilize protein skimmers to remove these proteins from the water. However, protein skimmers are not effective in fresh water.

If protein foam is present, it is an indication that the tank needs a good cleaning. Make sure the filter is clean, and remove any debris in the tank. Count your fish, as you may find that one has died and is hidden behind plants or rocks. A fish corpse is a rich source of protein, and frequently the root cause of protein foam.

Regular water changes, filter maintenance, and routine tank cleaning will ensure that you do not have a problem with protein foam in the future. It is also wise to visually check your fish daily to ensure none are missing.


If you have a male Labyrinth fish, such as a Betta or Gourami, the foam could be a bubblenest. Blowing sticky bubbles into a floating foamy nest is what they do to attract a mate.

They have no way of knowing that the only way a female is going to swim into the neighborhood is if you bring one home from the pet shop. A bubblenest is an indicator that your fish is quite happy and healthy, so consider it a good sign rather than a problem. Don't disturb bubblenests, even if there is only a single fish in the tank as it can be stressful for the fish.