Tips For Clearing Surface Scum/Film On The Top Of Your Fish Tank

Biofilm Make The Water Surface Looking Duller
Biofilm Make The Water Surface Looking Duller (Photo Copyright:

Did you peer on top of your fish tank, then discover some terrible stuff or film floating that look worse than an oil spill from the shipwreck on the sea?. This nuisance layer does not look right; it might threaten your aquarium populations.

Most aquarium keepers usually named it surface scum/film or biofilm. It is clusters of various microorganisms encircled by the slime produced by themselves, which is generally found stuck on the inert or living substrate in a fish tank.

Surface scum is a slightly usual thing in this hobby, and almost fish tank hobbyists had it in the aquarium. The reason that makes it like that is it can occur in the new tank setup in which the nitrogen cycling process is still not completed yet or even in the mature tank.

Today, we are going to teach you about this mysterious film, starting from what surface scum is, what causes it, its types of scum, its benefits and adverse effects from it, and how to prevent and get rid of it from our tank.


What Is Surface Film/Scum On Top Of Fish Tank?

Surface scum/film is usually found on top of a fish tank, like its name; it is also known as ‘biofilm.’ It is a massive and complex collection of bacteria (prokaryotes) and eukaryotes (other organisms such as algae, diatom, fungi, and other single-celled and multi-cellular creatures) that establishment a layer on any submerged water surfaces.

When you see it the first time, it may seem like gasoline on a wet surface, an oily layer that shimmers a rainbow color under the lights. In another case, it might look has a white or gray tint and is quite hard to see, forming clumps and then turning into some flakes if you touch it.

Depending on the causes, biofilms probably can show different appearances in one case to other ones.

An interesting fact is that surface scum is composed of many microorganisms type; they only take up around ten to forty percent of the surface film composition. And the remains, about 50-90% are formed of polysaccharides (from the Greek word σάκχαρον (sákkharon), which means ‘sugar’), which provides energy reserves for the microorganisms and act as a glue for those attaching on any surface objects in the aquarium such as leaves, decorations, hardscapes, water surface, etc.

There are no rules on how long it takes to grow in tanks. Every aquarium is different, just like every surface scum, because of its population numbers and combinations of various microorganisms that compose it. So, it can form over several hours to a couple of days on top of an aquarium.

Surface Scum With Foam At Top Of Aquarium
Surface Scum With Foam At Top Of Aquarium (Photo Copyright:


Common Causes Of Biofilm On Top Of A Fish Tank

As written above, if bacteria and other related microorganisms create the surface film on top of fish tank, the question is how they can exist in the aquarium?

The answer is ‘Dissolved Organic Carbon (DOC)’; it is the leading cause of biofilm in our planted aquarium.

So what is that? Simply, it is an organic matter that can pass through the filter media. Dissolved organic carbon acts as an energy source to support surface scum on establishment and reproduction. It can be earned from numerous sources; the surface film also can be stimulated for other reasons as the following below:


Organic Waste

Decaying plant materials, animal feces, and dead fish is the number one causing biofilm. In a younger aquarium where the biologicals have not matured yet, or in some tanks with weak/under-sized filters. It is frequently slowly absorbed by the filter, making it build up at the water surface. It contains a perfect oxygen level for supporting the microbial colonies growing and feeding on this waste.


Leftover Food

Any food type contains protein and fats; when you add it into your tank, it will dissolve and release materials as we tagged before and float to the surface.

This particularly becomes a serious issue when you feed too much, or some fish choose to unconsumed it, making the leftover food accumulate and release more fats and protein.

It might be worse if your fish’s diet prefers a highly protein or contains more oil on those food products.


Leaching Substrate

In some cases, utilizing a soiled-based product for the substrate can lead the oily film to go up. Soil contains a rich nutrient that helps in the process of forming a biofilm.



Be careful when selecting driftwood types for hardscape decoration. Bacteria can easily decompose and slowly convert it into nutrients (biofilm). In a high case, they can turn your tank water become biofilm soup.


Change In Plants Growth Parameter

Introducing new equipment or new light levels or new fertilizers, etc., makes the plants reprogram their cells to adapt to the new aquarium condition.

They will release some proteins into the water and then gather at the surface, usually as an oily layer.


Filter And Pump

A new filter can trigger a considerable oil slick because the pump and filter might have a small amount of oil over moving parts aiming to lubricate it. Aside from that, other oils that were remained during the manufacturing process.

In an old tank with a poor circulation system and gaseous exchange, microbes commonly settle at the surface, where it’s oxygen richest.


Excessive Iron

There is another type of surface scum that looks whitish, thinner, and even easily breaks when it is touched. This is caused by an iron bacteria (eisenbacteria) because the iron contents in the water have overdosed.


Constant Flux

An aquarium with high-growth speed, and high lighting with routine weekly trimming/replanting tasks, will usually be in a constant flux condition and may have surface film. Although, it does not has issues and matured.


Oil From Your Hand

You may not notice if pores in your hand skin naturally release an oil. It secretes a small amount and does not include oil from lotion or other moisturizers product you used.

When you do some activities that should contact with the water directly, such as trimming plants. During the process, the oil soaks into the water and constructs an oil slick on the above side of the fish tank.


Poor Planted Aquarium Location

You may not realize this factor; place selection can also be a problem of oily layer appearing.

A fine mist from perfumes or aerosol has to settle somewhere. It’s possible to locate it on your fish tank, then create an oil coating on the water surface.

Likewise, if you position your aquarium near your kitchen, an airborne grease from cooking can fall to the water surface, making oil slicks present.


Types Of Surface Scum/Film On Top Of A Fish Tank

Literally, it consists of various microorganisms. But, it can divide into two different types depending on which conditions are at hand, making the scum look more specific to an organism forming it. In this case, a particular organism may be predominant, such as a specific bacteria or blue-green algae.



A bacterial surface scum typically presents in a silvery-white appearance. Then if you touch them, they split immediately into smaller parts.

In another case, an oily-looking film is also considered as part of ‘surface scum.’ This form consists of fats and protein, so when you pierce your finger to it, it will close up again shortly. The bacteria that live on this scum type feed on the two previously mentioned substances.



These scum types can be identified as well because they have characteristics from the algae, which is commonly greenish or blueish in color. Moreover, you can see some clusters of foam or even giant bubbles with green or blue edges, indicating they are algae. Foams and bubbles are developed from the hampered gaseous exchange at the water surface.


What Is The Surface Scum/Film On Top Of A Tank Harm For Fish And Plants?

The biofilms are relatively innocuous, but if you let it for a long time, it can cause some adverse effects on the tank populations.

A reason why the surface scums can lead to an issue is that it can absorb the oxygen that should otherwise diffuse into the water, which means it can affect the vital gaseous exchange.

With its strategic position (on the surface), the microorganisms on the biofilm will get many benefits, such as accessing the unlimited oxygen in the air and consuming nutrients in the water which they need to develop.

It will cause the O2 and macronutrients level to decrease significantly entire the tank. Even in aquascape tanks which have many plants, they only produce oxygen during the light window, which is about seven to eight hours for most aquariums. But the fish, shrimps, bacteria, and other creatures consume it throughout the day.

This makes it clearer that an aquarium is dependent on the gaseous exchange on the surface for oxygen most of the time. You should know if the good O2 levels are essential to help the active bacteria colonies break down organic waste and keep algae away.

Other bad effects of excessive biofilm on the top of a fish tank include:

  • The plants only receive a small amount of light than they require.
  • Raising bacterial contamination in the aquarium.
  • It May causes asphyxiation to the fish, shrimp, and other organisms.
  • In some cases, it can increase the temperature, then lead an overheating in the freshwater aquarium.


What Is Biofilm On The Top Of The Fish Tank Offer A Benefit?

You must understand if a surface scum is part of the natural process, indicating how well your aquarium is balanced.

So in a well-stabled aquascape, it will disappear in a couple of days or even in a few weeks on its own.

Microorganisms that live in surface films, which are inhabited in every topside on a healthy and cycled planted tank, provide many essential nutrients such as amino acids, sterols, vitamins, and essential fatty acids that make them pretty important as an additional diet source.

Most shrimp hobbyists grow and keep biofilm to increase the success chance their shrimp tank in several ways like following here:

  • Leaf litter: It is a component that’s important for shrimp; put some dried cattapa leaf, alder cones, etc., and let it soak into the tank. During the decomposed process, microorganisms and biofilm will start to arise, then turn become food for them.
  • Wood: regardless of its function as decorations, driftwood (spider wood, cholla wood, mopani wood, etc.) also can release biofilm for shrimp, although it requires more time for it to form. However, it is still a better way to supplement them long-term.
  • Blanched vegetables: creating a biofilm with this ingredient is slightly rapid. It will form in several hours but do not leave it too long. It probably pollutes the aquarium water.
  • Powdered food: Bacter AE is a dried biofilm in powder form; this product is rich in nutrients that help promote and encourage biofilm growth rate and enhance shrimp fry survival levels.


How To Prevent Surface Scum/Film On Top Of A Fish Tank

Not only bad for aquarium populations, but biofilm is also horrible to see. It can lessen the aesthetic points of your fish tank.

Do not be panic, it relatively easy to control than other aquarium troubles such as algae. Although you are a newbie and do not have any experience, it’s no problem; following several tips below, you can keep away surface scum for a long time:

  • Maintaining your living aquarium in a balanced condition is the best way to avoid biofilm.
  • Keep in mind that if overfeeding is a source of disaster, ensure to be far from this bad habit and give your pets an amount of food as needed.
  • Put some clean-up crew to help overcome the overfeeding problem and remove detritus from your aquarium before it affects water quality.
  • Do not let the organic matter decompose and gather. Trimming the dying leaves with aquascape scissors and sucking up the rotting plants with a gravel cleaner.
  • Be aware of selecting driftwood types, make sure it’s fit for aquaria use and suitable with tank size, and do not over measurement.
  • Using a tank lid is suggested; it can block dust, airborne grease, and dirt into the aquarium.
  • Perform a routine water change and maintenance, clean all equipment, mainly the filter parts. An aquarium with slowly flowing water is prone to surface scum.
  • Recommended using high-quality soil such as Flourite Black Sand for the substrate.
  • Make sure your hand is clean and does not contain oil. Wash your hand with soap before contacting tank water directly if required.
Oily Film At The Surface Of Aquarium
Oily Film At The Surface Of Aquarium (Photo Copyright:


How To Get Rid Off Surface Scum/Film On Top Of Your Fish Tank

There are several methods that you can try for eradicating the biofilms in your aquarium, let’s read the guide below:


Surface Agitation

Installing an airstone or skimmer is a simple and effortless trick to resolve this issue. It has probably gone in several minutes or even hours, depending on outbreak levels and aquarium size.

Biofilm can not sustain itself in this situation even under weak water surface agitation. If you are keeping planted tank, you must know that a high surface agitation rate will reduce CO2 content significantly. So, balancing the system is the key to success in this way.

The safe method is using a skimmer. It is also compatible with freshwater and saltwater tank. There are two types of this tool, internal skimmer and external skimmer. Choose the one that fits your aquarium.

Note: surface agitation using airstone is does not work for marine or coral aquariums


Paper Towel

You just need a clean piece of tissue paper to eliminate the surface film in this technique. Just follow these steps below:

  • Drop a piece of paper towel and let it float on the surface for a few seconds.
  • Elevate it; you will see that all oil slick is sticking on this paper.
  • It is optional, and you can use another side of this paper to do the same job or take another paper.
  • After that, throw it away, then grab another one and never reuse it again. Repeat these series of processes after the biofilm disappears.


Bottle Method

Serve a large plastic bottle or jug, then sink it in a corner and let the oil layer and little water on the surface gradually enter the bottle. Redo the process until it totally does not exist in the aquarium.


UV Sterilizers

Eradicating any biofilm using UV sterilizers is more powerful and efficient. An ultraviolet light bulb (Visit Amazon to check out the price) can kill various microscopic organisms floating freely in the water. This is an excellent disinfection method because it can kill parasites, viruses, bacteria, and even algae.


Hydrogen Peroxide

If you found a stubborn surface scum and were doing all the above methods, but it still is not gone, the last way is to use a chemical.

It very risks your population and can break your tank entirely; if you are a beginner, avoiding this method would be better.

Occasionally an aquarist is forced to use this way. The first step is to enter 3% hydrogen peroxide solution into a spray bottle, then straightforwardly sprayed to the surface scum on top of the aquarium. Be careful and do not give too many doses.

If it gets on pets (fish, snails, shrimp, etc.) or plants, it can hurt or even kill them.

Note: Hydrogen peroxide is generally used as an antiseptic, oxidizer, and bleaching agent.


Eliminating Submerged Surface Film

The first method is you can clean it with a toothbrush, after that rinse in fresh water. Next, the second is keeping some tropical aquarium snails, shrimps, or otocinclus fish. They are an ideal species for eating algae and underwater biofilm.

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