Even the most stunning aquarium can look unsightly when a slimy, oily film forms on the water surface. This can be a bit alarming the first time you notice it and you may have wondered how to remove film on top of the fish tank.
Film on top of a fish tank is usually caused by too much organic waste in your aquarium, such as extra food, fish poop, and dead fish. There are several ways to remove it, but the easiest is by simply using a paper towel (if it is not too severe).
There are other causes of oil films in your aquarium water, some of which need different methods to eliminate. But don’t worry, we’ll be going over all of this below to help you get rid of pesky surface scum for good!
What Is The Film / Oil That Forms On Top Of Fish Tanks?
The oily film that forms on the top of fish tanks is known as surface scum. It looks like a milky, oily, or slimy coating on the water surface. There are a few different types of film that can develop at the top of your aquarium water, including protein film, algae film, bacterial film, and an oil slick.
This video explains how to prevent and stop an oily layer from building up in your tank:
Protein film (also known as protein foam and protein scum) looks like a white, foamy substance on the surface of the water. It is common in aquariums as it is caused by organic waste in the tank, such as feces, dead aquatic life, and leftover food.
This leads to the formation of tiny air bubbles that can smell pretty foul.
One of the easiest ways to identify whether the surface scum in your fish tank is due to algae is by simply looking at its color. Algae film is a bright green hue and will look very slimy. Your setup may also have green water (like pea soup).
Algae in the aquarium is usually caused by too many nutrients (usually due to poor tank maintenance and overfeeding) or excess light.
A bacterial film or bio film on the surface water is normally a white or silvery shade. If you touch it, it will break apart into tiny segments. The substance develops as a result of bacteria eating the excess organic waste in the water.
This type of oil film is particularly common in planted tanks that are treated with fertilizers as it is usually caused by a buildup of iron in the water.
In these cases, it’s best to reduce the amount of iron in the water by switching to a less iron-heavy fertilizer.
Oil slicks at the top of your tank’s water have a rainbow color in the right light. They are most commonly caused by oil, such as airborne grease or grime from your hands.
What Causes Film / Oil On Top Of A Fish Tank?
There are various causes of film formation on the surface of an aquarium:
- Uneaten foods
- Dead fish
- Oil from your hands
- Airborne grease (from poor tank location)
- Too much iron
- Aquarium equipment
- Poor water quality
Too much fish food or poor-quality foods can lead to protein films in your aquarium’s water. Most fish food contains fat, but lower quality brands often contain more of it.
If you overfeed your fish or give them oily food, the fats and proteins in the fish food will float to the top of your tank. The best way to counteract this is to reduce your fish’s feeding time and the amount you give them. Switching to a premium food brand can also be helpful.
Fish poop contains a small amount of fat, which when left to build up in your tank, can lead to an oil spill on the surface of the water. Regular water changes and gravel vacuuming is important when keeping fish to remove excess waste.
When fish pass away, their body leeches fats and oils into the tank water, which can result in an oily substance appearing on the surface of the water. You should always remove dead aquatic life from your setup as soon as possible as it can lead to ammonia spikes.
One of the most common causes of an oily film on surface water is oily hands. As a fishkeeper, it’s normal for you to get your hands wet, whether that’s to clean the aquarium glass, feed your fish, perform a water change, or prune your plants.
The pores in your hands naturally secrete oil, so when you dip them into your aquarium, the oil can wash into the water. The amount of grime on your hands will be more if you regularly use moisturizers, too.
Before you put your hands into your tank water, thoroughly wash, rinse, and dry them.
Airborne grime or grease can result in oily film in freshwater and saltwater aquariums, such as from perfumes, aerosols, or dust particles. Alternatively, if your tank is your kitchen, oil from cooking can find its way into your fish’s enclosure.
You should move your setup to an area where there is less risk of dust or grease getting inside your tank. In addition, avoid using aerosol sprays around your fish’s habitat. Using a tank hood or cover can be useful for keeping your aquatic pets safe from pollutants outside the enclosure.
High Levels Of Iron In the Water
If there is too much iron in your water, then it can contribute to the formation of an oily layer caused by bacteria in your water. This is common in a planted freshwater aquarium, especially if you use fertilizers.
Switch to a different fertilizer brand that contains less iron or reduce the amount you dose your tank.
Filters And Pumps
Aquarium equipment like filters and pumps often use a small amount of oil to operate, which may lead to a thick layer of surface scum. A new filter may also contain a bit of grime left over from the manufacturing process.
Clean any new tank equipment before putting it in your setup to wipe away excess grease.
Poor Water Conditions
Poor water quality in general can lead to oil film forming on the water surface. This is common in both new tanks and mature aquariums that have been left dirty for long periods (old tank syndrome). Regular water changes and gravel vacuuming is key to keeping your tank clean.
You should perform a water change at least once a week (more if your setup is overstocked), making sure to vacuum the substrate with a gravel cleaner. You should also clean your aquarium equipment and filter media regularly using old tank water (never use tap water).
How To Remove Film / Oil On Top Of A Fish Tank (3 Methods)
A greasy substance in your aquarium not only looks unpleasant, but it can also harm your fish if it is left unattended. It’s important to eliminate it as soon as possible to keep your tank clean and your fish healthy.
Fortunately, removing the film at the top of the water surface is straightforward and can be done in several methods depending on the severity. But first, you’ll need some supplies!
- Paper towels
- Air pump
- Surface skimmer (freshwater tank) or protein skimmer (saltwater tank)
Once you have the supplies needed for getting rid of pesky grime at the top of the water surface, you can start the removal process. There are a few different ways to do this, so if the film is particularly persistent or thick, you might want to attempt all of them.
Method 1: Use Paper Towels
The most effective way of eliminating surface film in a tank is by using paper towels. A paper towel will absorb any grime it touches and leave your aquarium water sparkling clean again!
First, turn off all your equipment (filter, heater, light, etc), then place a paper towel over the top of the water. After a few moments, take the paper towel away (make sure you don’t squeeze it back into the water) – you should see the film stick to the material.
If the oily grime in your fish tank water is particularly thick, you might need to do this several times with multiple paper towels before you start seeing a difference.
Don’t worry if you don’t have any paper towels on hand – you can also use a clean jug to drain the oily gunk.
Method 2: Add Water Movement
Surface agitation is a great way to clear oily films in your setup. This can be achieved by adding an air pump into your tank or by moving the nozzle on your filter intake towards the water surface.
The water movement will help prevent stagnant water and mix up the oils in your aquarium. Ample surface agitation is also great for your aquatic pets as it increases oxygen levels in your aquarium.
If there is an oily section in a small area of your aquarium, it might point to a dead zone in your setup where there is little water circulation. Use an air pump or change the location of your filter to allow for more surface agitation.
Method 3: Use A Surface Skimmer Or Protein Skimmer
Surface skimmers are useful for freshwater tanks as they help keep the water surface clean by removing oily films.
Protein skimmers like the Coralife Biocube Protein Skimmer are slightly different and are commonly used in saltwater tanks for getting rid of proteins and organic compounds in the water.
Protein skimmers aren’t effective in freshwater tanks unless there is a lot of protein in the water. They’re invaluable if you have a marine tank, though!
If you have a freshwater setup, consider investing in a surface skimmer to keep the water surface free of debris and oily gunk.
There are a lot of surface skimmers available, but the Aquatop Aquarium Surface Skimmer is a particularly great choice as it’s compact, easy to install, and has a flow rate of 65 GPH.
How To Prevent Film / Oil From Forming On Top Of The Tank
While removing greasy films on the water surface is relatively easy, the best way to stop this oily substance is to prevent it from forming in the first place!
Add Surface Movement
Ensuring your tank has ample water surface movement will help keep aquarium films at bay as it will help mix the oils into the water. A powerful filter or air pump will assist with water circulation to prevent dead spots in your setup and increase oxygen levels.
Perform Regular Tank Maintenance And Water Changes
Poor water conditions can contribute to an oily water surface as there will be an influx of organic waste in your aquarium. You should keep your tank equipment clean and commit to frequent water changes to remove excess waste in your aquarium and promote stable water chemistry.
Perform a water change at least once a week – remove one-third of the water and replace it with clean dechlorinated or distilled water. Vacuum the substrate once a week with a gravel cleaner to get rid of poop, decaying plants, and debris.
You should also check your aquarium at least once a day for dead aquatic life, especially behind blind spots like the back of your filter or among aquarium decor.
If you have a lot of live plants in your setup, make sure you trim and prune them often and try to reduce the amount of iron-heavy fertilizers you use.
To prevent dirt and grime from transferring from your hands to your fish’s enclosure, wear gloves when you need to do work inside your tank. Alternatively, avoid using hand lotions and moisturizers on the same day you need to do tank maintenance.
Wash your hands and rinse them thoroughly before you care for your fish.
Stop Overfeeding Fish
Overfeeding fish is one of the main causes of an oily water surface, so make sure you only offer your aquatic pets as much food as they can finish in a minute or two. After this duration, remove anything your fish have left with a net.
In addition, try to feed your tank’s inhabitants high-quality brands that don’t contain a high amount of fat.
Is The Film Harmful To Fish?
Aquarium grime or film itself is not harmful to fish, but its presence can be a sign of something wrong in your tank, such as too much organic waste in the water.
In addition, if the grease is not removed swiftly and is left to build up in a fish or shrimp tank, it can reduce the amount of oxygen in the water.
The oily substance serves as a barrier that blocks oxygen from entering the tank, while also locking carbon dioxide inside. This can cause your tank’s inhabitants to suffocate.
How Long Does It Take To Remove Film On Top Of A Fish Tank?
It doesn’t take long to remove film in your aquarium, perhaps 5 minutes at most if you’re using paper towels and the substance isn’t thick. A strong air pump and good water circulation should mix in the oils and clear the film within 10 to 15 minutes.
Can The Film Go Away On Its Own?
In an established setup with stable water parameters, biofilm or surface scum can go away on its own. This can take anywhere from a few days to a few weeks. Certain fish, aquatic snails, and shrimp will eat biofilm, so they can be valuable assets to your tank.
Film at the top of your setup water can be unpleasant and worrying, but it’s a dilemma that most aquarists will face at some point. It’s typically caused by too much organic waste in your water, such as excess feces or dead fish.
While it can be dangerous if it’s left to build up for a long period, removing it is very simple and doesn’t require much work. Paper towels, water agitation, and a surface skimmer or protein skimmer will effectively get rid of the grime, allowing you to have a clean tank once again.
You can stop the development of wet surface scum by simply keeping on top of tank maintenance, as well as ensuring you have good water movement. Washing your hands is also a good idea before putting them in your aquarium!
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