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7 Reasons Why Your Aquarium Water Has Bubbles or Foaming

Have you ever seen bubbles or foam in your aquarium water and wondered if it’s safe for your fish? Bubbles can happen for many reasons — some of them good and some of them bad — so let’s talk about what to watch out for and how to fix the problem if needed.

1. Normal Bubbles from an Air Pump

Of course, the most obvious reason for bubbles is that you are using an air pump that sucks in air from outside of the aquarium, pushes it through airline tubing, and pumps it into the water. Typically, the air pump is connected to an air-driven device — like an air stone, sponge filter, bubbler, or bubbling aquarium decoration. These bubbles should be transparent and pop immediately once they reach the water surface.  Another normal instance of bubbles is if you have a high tech planted tank and are using CO2 injection. In these systems, a diffuser is often used to break up the CO2 gas into tiny bubbles that will quickly dissolve into the water.

Aquarium Co-Op sponge filter - lifestyle

Normal bubbles from a sponge filter

2. Micro Bubbles After Water Changes

After doing a water change, sometimes you may see micro bubbles covering all the surfaces inside the fish tank. During the winter, water coming from the underground pipes outside can get very cold, so the water heater warms up the water so that it is the right temperature for your tropical aquarium. Hot water cannot hold as much oxygen as cold water, so when the water temperature is raised, dissolved gases get released into the water and form little bubbles all over the glass, substrate, plants, and decorations.

This phenomenon is nothing to worry about, and most of the bubbles should disappear after a few hours. However, if there are an abnormally high number of bubbles on the glass, it could indicate that not only was there a wide temperature difference, but also a large volume of water was replaced. Keep a closer eye on the tank for the next few hours or days because huge water changes can cause big swings in water parameters, which in turn can affect your fish’s health.

micro bubbles on plant leaves

Micro bubbles cling to surfaces, like plant leaves

3. Fish Medications or Chemicals

Certain fish medicines have been known to cause foaming because they change the viscosity or thickness of the water. If you have an air stone or sponge filter in the tank, normally the bubbles would pop right away, but when the water is thicker, it takes longer for the bubbles to disperse. Foam caused by these medications tends to form clear, transparent bubbles, but if the bubbles have an oily, iridescent sheen, it could be caused by soap or other cleaning products — which are very dangerous to fish. If something in the fish tank needs to be cleaned, most of the time you can simply rinse it with water. If it needs to be disinfected, wash or soak it with a diluted bleach solution, rinse it with clean water, and make sure the item is completely air-dry before putting it back in the aquarium.

foaming in planted tank

Bubbles caused by medication don’t pop as quickly

4. Oil Slick on the Water Surface

You may notice a gooey, translucent biofilm can form on top of the water and trap bubbles that would normally float up and pop at the surface. This filmy layer can be caused by the oils in fish foods, oils from your hands, and other organic compounds in the water. While some hobbyists like to use a paper towel to soak up the biofilm, this is only a temporary solution. The oil slick is visible due to a lack of surface agitation and proper gas exchange, which is necessary so that more oxygen can enter the water for your fish to breathe. Use a sponge filter that creates bubbles to agitate the water surface, or aim the filter’s output at the surface to help dissipate the oil and increase oxygenation. Also, remove overgrown floating plants that are hindering surface agitation.

5. Excess Ammonia

If you have ever visited a cattle farm, you may notice that it can create a lot of animal waste runoff that enters the nearby waterways, resulting in foaming water. In the same way, you may see foaming in your aquarium if there is an abundance of toxic ammonia waste in the water. Ammonia can be caused by a heavily stocked aquarium, feeding too much fish food, or even leaves and other debris falling into an outdoor mini pond. As with fish medicine, this phenomenon is only apparent if you have a sponge filter or something creating bubbles in the water. If you see unusual foaming in the absence of medication, it may be a sign of excess ammonia or other harmful chemicals in the water, so use your ammonia and multi-test strips to find out what is going on.

agricultural runoff can causing foaming

Excess animal waste in water can cause foaming

6. Bubble Nests

Lest you think there are no good reasons for seeing bubbles, let’s talk about the bubble nests created by betta fish, gouramis, and other bubble nesters. These males create bubbles with their saliva and pile them all together in a tranquil corner, next to a floating plant, or somewhere there isn’t a lot of surface agitation that will disrupt all their hard work. (If you accidentally scatter your betta’s bubble nest during a water change, no worries — the males make new ones all the time whenever the old nest becomes worn out.) During breeding season, the male will court the female and use his mouth to gather up the eggs she drops after mating. These eggs are spit out into his bubble nest, which he will aggressively guard until they hatch and the babies become free-swimming.

bubble nest created by male betta fish

Male betta fish guarding his bubble nest

7. Pearling Plants

During the daytime when plants absorb light to photosynthesize, they actively consume carbon dioxide and release oxygen. When the water becomes overly saturated with dissolved oxygen, any additional oxygen produced by the plants can be visibly seen as a stream of tiny bubbles released from pores in the leaves. You may also see bubbles produced by algae that is also photosynthesizing. While algae may not be the most attractive sight, they can still be good for the overall aquarium ecosystem since they produce oxygen for the fish to breathe and absorb nitrogen waste compounds produced by the fish.

pearling aquarium plants

Pearling is a good indicator of high oxygen levels

Bubbles in aquarium water can be a sign that something dangerous or something beneficial is happening in the fish tank. To learn more, check out our library of articles that will help you better understand your aquarium water and how to keep it safe for your fish.

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