White foamy bubbles covering fish tank – What to do?

By Nadine Oraby | 2020 Update

You always make sure your aquarium is squeaky clean.

But one day, you notice a patch of foamy bubbles floating on the water surface.

What could those foamy bubbles be? A patch of foamy bubbles in a fish tank could be one of four things. They could be caused due to agitation, soap residue, protein accumulation, or might simply be a bubble nest.

However, the good news is that two of these are usually harmless. But you still should be aware of the source of these bubbles.

Keeping that in mind, let’s get into some detail:

Why are there bubbles covering my fish tank?

Before we dive in, let’s get one thing straight:

Not all bubbles in a fish tank are harmful. Mostly, bubbles are created by water filters as well as air stones that you’ve added in the tank.

These are typically small but in large quantities, and will usually pop once they hit the water surface. You have nothing to worry about these kinds of bubbles as they actually let more oxygen enter the water.

Another type of bubbles you will commonly notice in aquariums are those on the plants. These small bubbles are usually attached to the leaves like small pearls.

This happens when the aquatic plants produce oxygen through photosynthesis which causes the plants to convert CO2 and nutrients into oxygen bubbles. This process is known as pearling and is also a good sign that your plants are growing well.

Both of these types of bubbles are pretty common and completely harmless. However, sometimes you’ll notice that the bubbles stay for a little longer or turn into patches of foam at the surface. So now, let’s take a look at what causes white foamy bubbles to collect on the surface of a fish tank.

Causes of white foamy bubbles covering fish tank

Like we explained earlier, white foamy bubbles could be the result of one of four occurrences. Out of the four, two are totally harmless and quite normal. However, two of them require attention and pose a risk to your fish and need immediate attention.

Surface Agitation

It’s a very normal thing for foam to collect on top of the water surface when it’s agitated. Think of it this way:

When you shake a bottle of water or any other liquid, some foam always collects at the surface of the water which disappears briskly. So when you add or fill your aquarium with water, the same process happens.

This type of foam is completely harmless and usually consists of bubbles that disappear after a while. However, if the bubbles are irritating you, just add the water more gently and as close as you can to the surface to avoid the creation of any bubbles or foam.

Another cause of surface agitation can be a displaced water filter. Every water filter has an outlet from where the clean water falls back into the tank after it has been purified.

Sometimes, this outlet can be quite a distance above the surface of the water which again constantly creates bubbles which can gather in the form of foam. To overcome this, make sure the outlet is just the slightest distance away from the water surface to avoid the creation of such foam.

Bubble Nests

Another explanation could be that the white foamy bubbles on your tank’s surface are actually bubble nests. Bubble nests are a patch of tiny bubbles that fish blow with their saliva and create a whole bunch of them for reproduction.

These bubbles are created so that a female fish can deposit her eggs in it while they incubate and hatch. Bubble nests are commonly produced by two species, Bettas and Gouramies. So if you’ve got either of them, chances are you’ve got a bubble nest floating on your water surface.

Thankfully, these bubble nests are completely harmless and won’t interfere with any of the other fish as well. These bubbles might also contain some debris, so don’t worry about whether there’s something wrong with your fish or not.

Also, if you’re wondering why your male Betta or Gouramies are making bubble nests even though there aren’t any females, it’s totally normal. The males do this to attract females near them, whether you have any in your tank or not.

Soap Residue

Now here’s where things start going south. If you think the foam on your water surface is due to leftover soap residue, you need to take immediate action to protect your fish from harm.

The easiest way to recognize bubbles made by soap residue is to look for a rainbow tint in the foam or bubbles when light is reflected on them. If you do see that rainbow tint, chances are you’ve left soap residue in your tank.

In this case, you should probably remove your fish from the tank as soon as possible as soap can be fatal to your fish. Shift all of your fish into another tank or a clean bucket of water as you have to do a complete cleansing of your tank.

Drain all of the water and clean each and every piece of decoration thoroughly to remove any leftover soap residue. We also highly recommend washing the water filter as it may have absorbed and collected soap from the soapy water and might release it back into the new water that you refill.

Once you’ve cleaned all the things, you can rearrange things back to the way they were. Make sure to fill the tank with the same type of water as before. Also, you should preferably wait a while after restarting the filter to look for any new patches of foam to be sure that there’s no more soap left.

After you’ve done everything and placed the fish back into the tank, think why the soap was in there the first place. Most of the time, soap residue can transfer from a bucket you used to fill the tank with water. Or some soap residue can be left on some decorations when you cleaned them.

No matter what the reason, always be very careful about leaving soap in the tank. Even just a little amount is enough to cause life-threatening damage to fish including damage to their gills and breathing.

Protein Accumulation

If not anything else, then the foam in your tank could also be the result of too much concentration of protein in the water.

When bubbles form and there’s a lot of protein in the water, the protein covers the bubble and prevents them from popping. This can cause a patch of foam to form and it usually has a bad stench to it.

Now protein can accumulate in your water for a couple of reasons. It can be due to the excess food that’s starting to rot, general uncleanliness of the tank, or even due to a dead fish that’s decomposing.

If you regularly add excess food and can usually see it floating, chances are this food will start to rot, turn into protein and mix into the water. This is more probable if you frequently feed your fish live food like worms. Always remove excess food as it can make the water dirty really quickly.

Another reason could be that your tank is just generally unclean. It’s very important to do regular water changes as well as cleaning the water filter frequently as it starts collecting grime. Make sure that you also clean the gravel in the tank from time to time as it can also collect a lot of filth.

Lastly, and most importantly, the excess protein could also be the result of a decomposing fish. Sometimes, fish go hide into a rock or some corner and die. Although they’re not visible to the eye, they start decomposing which causes protein to buildup in the tank water.

Therefore, it’s important to keep a count on your fish, clean your tank regularly and remove any excess food from the water.


These are the most common causes of foamy bubbles in a fish tank. Probably the best way to prevent such problems would be to regularly clean your tank and do water changes every once in a while. Not only do these help prevent the buildup of germs and filth in your tank, but they also keep your fish healthy and lively.


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