Waking up one morning and seeing a build-up of what looks like an oily film on top of the water of your fish tank can be a little worrying. Especially if it’s your first time encountering this issue…
In general, getting rid of biofilm on your aquarium’s surface is very easy. You can use surface skimmers, create more surface agitation, or manually remove this protein film with a paper towel. Once you remove the surface scum, you will want to investigate the root cause of the issue.
This surface scum is sometimes referred to as biofilm or protein film and can look like an oil slick has formed on top of the water of your fish tank.
It’s easy to take care of, and you usually won’t run into this issue if you are running a surface skimmer or a filter with a built-in skimmer.
My recommended filter with a built-in skimmer is the Tidal HOB filter. You can check the prices on Amazon here.
But if you don’t have a protein skimmer or a good amount of water movement on the surface of your aquarium, then a thick layer of oily film can start to form.
Below, I’ll talk about what causes this oil film to start forming, whether you should be concerned about it, and how to remove this film from the surface of your aquarium water…
What Causes Oily Film To Form On Top Of Fish Tank Water Surface
The formation of biofilm (also referred to as protein films, oil films, oil slicks, surface scum, etc) is from the build-up of microorganisms on top of the water surface.
These microorganisms feed on the organic wastes within your aquarium water.
It’s completely normal to get a small build-up of this film on the surface of your fish tanks. This is especially true if you have low surface agitation and are not running a skimmer.
But if you find yourself dealing with a thick layer of this stuff and dealing with a constant battle with this surface scum, then you need to lower the organic wastes being built up within your fish tank.
This can also be a sign of poor water quality within your tank. (Unnatural thick layers of oily film, bubbly water, or a strong foul odor. Can be signs of an underlying issue within your fish tank.)
Here are the common reasons why you may have an abundance of surface scum on top of your aquarium water…
Too Much Fish Food Left Uneaten
A common reason the water surface of your aquarium may start to look like an oil slick accident has just happened is because of overfeeding your fish food and not cleaning up the uneaten fish food left behind.
If you tend to go a little overboard during feeding time, then lots of uneaten fish food can slowly build up within your tank, causing the perfect environment for oily films to start from the top of your tank.
Decaying Dead Fish Somewhere In The Tank
I get it…
Sometimes, it can be hard to notice a dead fish in your fish tank, especially if you have nooks and crannies where only your fish can go in and out.
But if you leave the bodies of your dead fish to rot and decompose in your tank, it can cause lots of unwanted problems down the road.
A build-up of surface scum is the least of your problems…
Dead fish can cause a spike in ammonia, and your tank cycle can crash, leading to other problems.
Too Much Fish Waste Building Up Within Your Fish Tank
This sort of goes hand in hand with over-feeding your fish. But if you let fish poop build up in your tank, then this is another reason why an oil film or protein film can start forming.
If you are overfeeding fish food, this will cause your fish to produce more fish poop.
Also, if you skip your water change or just don’t clean your substrate very well, this can be another reason why fish poop can start building up in your tank.
Not Enough Or Inefficient Filtration
Like I said before, a small amount of oil film on the water surface of your tank is completely normal.
But if you don’t manually clean this oily film or have a filter or skimmer that does it for you automatically, it can start to build up over time…
Even running a sponge filter with an air pump can create enough surface movement for surface scum to disappear in a healthy aquarium.
The Oil From Your Hands
Sometimes, the oily film being formed on top of your aquarium water is caused by the oil from your hands.
This is something to keep in mind if you are putting your hands into your fish tank often. The natural oils from your skin and even the oils from skin products like lotions can cause a build-up of an oil film.
Just make sure you clean your hands properly and avoid putting your hands in the aquarium water if you think you may have chemicals or lotions on your skin.
You can also use gloves if you want to be extra cautious.
Airborne Grease And Other Contaminants Falling Into Your Tank
Last but not least…
One reason some people may not think about is the placement of their aquarium. Even though it sounds weird, the placement of your tank can cause it to have an oil slick on your aquarium surface.
This is common for people who have their fish tanks located in or near the kitchen of their home.
Airborne grease from cooking sprays, cooking oily food, and oil released/burnt off during cooking, in general, can fall on your aquarium surface and cause oil slick problems.
So make sure you keep the placement of your aquarium or planted tanks in mind…
How To Remove Bio Film On The Surface Of Your Fish Tanks
Now that you know what the main causes are for biofilm or that oily layer of film starting to form on your water’s surface, let’s talk about the three different ways to remove it.
Use A Surface Skimmer To Clean The Water Surface
I’ll be honest; the easiest way to never have to deal with surface scum is to use a filter with a built-in skimmer to take care of any film build-up on the surface of the water.
You also have the option to run a separate protein skimmer. Surface skimmers can clean your surface water whenever it starts to build up a layer of film.
You don’t have to run this 24 hours a day. You can run it once a week (or whenever you find it necessary to do so) for a few hours or until it clears all the surface scum from your tank.
Create More Surface Movement And Agitation In Your Fish Tanks
Another way to deal with surface scum or prevent the build-up of oily films is to have sufficient water surface movement and agitation.
A quick and easy way to do this is to run a sponge filter in your tank. (but you can also increase the flow of your filter, use power heads, etc.)
I had a 14-gallon cube tank with very little flow and movement. And a thick layer of biofilm would start to form after a few weeks…
I decided to put in a sponge filter because I wanted to have a second filter I could use to jumpstart new tanks or run my quarantine tanks.
However, the air bubbles from this sponge filter created enough surface water movement in my tank that the film on the surface of my fish tank stopped forming.
Manually Remove Surface Scum With A Paper Towel
Lastly, you can always remove surface scum the old fashion way with the use of paper towels.
This process can be time-consuming and ineffective, especially with larger tanks. But if you have a smaller tank, then using paper towels to remove surface scum can be your best bet.
The easiest way to do this is to lay the paper towel on the water surface of your tank and then quickly remove it to try and catch the oily film from the surface.
Throw out that piece, then repeat it until your entire tank is clean.
I know this process can be a bit wasteful and time-consuming. That’s why I just recommend having a skimmer that can do all the work for you.
Should I Be Concerned If An Oily Film Forms On Top Of The Water In My Aquarium
There is no cause for alarm if you have noticed that an oily film has started forming on your aquarium’s surface.
In general, biofilm or that oily film on the surface of your aquarium poses no immediate threat to your fish or other livestock within your fish tank. But if left to grow and build into a thick layer, then this film can start to deplete oxygen levels in your tank and suffocate your fish.
The surface of the water in your aquarium is responsible for gas exchange. If you let this film build-up, it can prevent the gas exchange from happening, and your tank can slowly become depleted of oxygen.
But if you regularly maintain your tank, have sufficient water movement, and don’t let this film get out of hand, you should have nothing to worry about.
What To Do If Biofilm Starts To Form On My Aquarium Driftwood
The surface of the water in your fish tank isn’t the only place where biofilm can start to grow.
Biofilm can start to grow on your hardscape, especially if you have driftwood or other types of wood within your fish tank.
You can read this post about biofilm on aquarium wood to learn more about how to get rid of it.
Getting rid of that kind of biofilm is a bit different than dealing with surface scum. Be sure to check out that article if you are dealing with it in your aquarium.
Final Thoughts On Getting Rid Of Water Surface Scum And Oily Films In Aquariums
This wraps up what I have to say about dealing with surface scum within your fish tanks.
If you are dealing with this issue, make sure you address the root cause of the problem…
But don’t worry, this film is harmless and usually just a bit of an eyesore. If you neglect it and allow it to build up, then that is a different story, and it can start to harm your livestock.
But the good news is…
Removing the film is easy to do, and I recommend using a filter with a built-in skimmer to handle it for you.
I hope this post was helpful and able to answer any questions you might have had about this topic.
I wish you the best on your fishkeeping journey and hope to see you in another post!