White Film on Top of Aquarium Water [4 Easy Solutions]

Are you observing a white film on top of the aquarium water and pondering why this awkward thing suddenly appeared? Though it is not a very common problem, you are not the first person facing it.

The white film layer’s appearance can be slightly different from case to case, but more or less, it looks like an oily layer. Sometimes it is a white layer or greyish white, or it can be just like floating oil layers reflecting rainbow colors under lights.

I’ll talk about this mysterious white film on top of aquarium water, and hopefully, all your confusion will be overcome.

What is this white film?

The white film on top of aquarium water is nothing but an oily protein layer. The primary source of it is bio fat, and so, this white film is often referred to as a ‘biofilm.’

It occurs for several reasons that I will discuss in later sections.

When it appears as clear as oil, it is sometimes difficult to identify. Oily protein matters can also form a glossy coating on top of aquarium items like decors and inside glass walls.

Why is this white film bad?

White Oil Like film on top of aquarium
White Oil Like film on top of aquarium Owner: Miranda Renee

Though white film on top of the aquarium water is not something terrible, not a good thing, either. You have at least two reasons to combat it.

It hinders air-water contact:

The aquarium water must come in contact with the ambient air. Fish need oxygen to survive, and they collect it from dissolved oxygen in the water. Oxygen dissolves in the water from the air contact.

A layer between the aquarium water and air obstructs oxygen entrance into the water. Thus dissolved oxygen level of aquarium water can go down. Fish may suffocate at a lower oxygen level and die!

Simultaneously, CO2 produced from fish respiration raises the CO2 level of water unless dissolved CO2 evaporates into the air. The white layer also creates restrictions for CO2 to get released into the air. Thus trapped CO2 in the aquarium water can kill your fish.

It looks unpleasant

The second reason is aesthetic, and to me, it is also vital. A healthy-looking aquarium can give you a pleasing feel. Fishkeeping is your hobby and the source of refreshment. A neat and clean aquarium is desirable, so you should not let surface scums ruin your aquarium’s beauty.

Reasons for forming the white film on the aquarium water surface

People sometimes get confused about the sudden appearing this greasy layer. I have read a case on a forum, and I found it interesting.

An aquarist was away from home, and his wife was deployed to take care of his aquarium fish for six months. During this long period, she just fed the fish every few days and did nothing but water top-up when required. Everything was going smoothly.

But after the aquarist returned home and started feeding the pets regularly with other maintenance activities, he observed forming a white layer! It seemed strange to him.

I thought about the case and realized that probably the extra food he started to provide for his fish’s wellbeing was the protein layer’s primary causing factor. There might have some other factors. Let’s discuss one by one:

8 reasons for forming white film on top of aquarium water

1) Fish food

As I said, fish food could be the major contributing factor to forming a fatty layer. Especially protein-rich food like frozen bloodworms is a significant source of oily matter.

If you overfeed your fish, they can’t consume them all. Food leftovers first dissolve and then decompose.

When fatty food dissolves in the water, fat comes out to form a white layer on top of the water.

A protein-rich food is essential for fish’s growth, so you cannot stop feeding it. But you can ensure no food leftovers by providing less.

White film layer on top of aquarium
White film layer on top of aquarium Owner: Blaire Graniero

2) Overstocking

Overstocking causes more fish poops. Fish poops are oily. Fish’s digestive system breaks down food into protein and oil. Fish poops go nowhere but stay in the aquarium. 

In normal circumstances, fish waste is manageable by routine cleaning. But if you overstock, fish will produce a lot of oily waste. And if that happens, a white layer or oil slick forms. 

Therefore, I recommend stocking in the right proportion to avoid this happening.

3) Low turbulence in the water

Where the aquarium owner maintains a low water circulation flow or has no airstone to produce bubbles, white film formation is a more possible scenario there.

Continuous bubbling can somewhat be capable of throwing oily matter out of the water. An air pump adds extra oxygen to the water, and it is also beneficial in fighting against white films.

4) Inadequate chemical filtration

A typical chemical filtration system consists of carbon media, which can absorb oily matter. Sometimes people give more emphasis to mechanical and biological filtration than chemical filtration.

If your system doesn’t have adequate chemical filtration, keeping all protein and oil sources uncontrolled might be a reason for a layer formation on top of the water.

5) The water source

If you use water that contains any dissolved mineral, it can be oxidized over time and form a white layer. Some iron compounds that are present in tap water may have such characteristics.

Initially, these compounds remain dissolved in the water. But they react with oxygen and get converted to some other products that form a thin layer on the water’s surface.

It’s always better to treat the tap water with a water conditioner to remove heavy metals, chlorine, and chloramines. Properly treated tap water will help you prevent any issues with the water.

White film formed on the water's surface
The white film formed on the water’s surface

6) An oily working hand

It is not good to engage in aquarium work with bare hands. The aquarium water carries germs that can be harmful to humans also. And at the same time, oily matter can contaminate the aquarium water.

Your hand secretes oils naturally, though small in quantity. Also, unwashed hands can carry oil from external sources also.

So it is quite possible that sinking your oily hand frequently in the aquarium water eventually forms an oil slick, especially in small aquariums with a low volume of water.

7) Decomposed dead fish

If fish die in the aquarium, remain unnoticed, and their body decomposes, body fat will come out from decomposed dead fish.

So, you can imagine what the next thing is going to happen. Fatty matters start floating on top of the aquarium water and form an oily white film.

This reason is feasible in larger aquariums with lots of fish where dead fish is difficult to notice.

8) External greasy matters

External airborne oily things can enter your aquarium if it is an open-top. The location of the aquarium is also a vital consideration for this point.

If the fish tank is located near any roadside open window or near the kitchen, it is more likely that fine mists of organic matter contaminate the aquarium water.

Perfumes, aerosols, or cooking oil vapors from the kitchen entering the aquarium may form an oily film on top of the water.

I have a separate article on where to place the aquarium in a home. I invite you to read that article to check if there is an issue with your aquarium placement.

How to get rid of white film formation on top of aquarium water

None would appreciate a white film on top of the aquarium water, as it looks unpleasant and at the same time could be unhealthy for fish. Here I am suggesting four solutions to get rid of it.

how you get rid of oil slick

1) Have a powerful air pump with an airstone

Having an air pump is probably the easiest solution to this problem. Keep strong water flow in the aquarium and have an airstone to form bubbles.

Continuous bubble formation on the water surface will effectively prevent white film or oil slick formation on top of the water.

You can use a filter with a strong output or a spray bar to keep a high water current in the aquarium.

Alternatively, you can enhance the water flow by adjusting the flow nozzle’s direction, for instance, pointing it to a surface.

A newly bought aquarium air pump
A newly bought aquarium air pump

2) Have a surface skimmer

A surface skimmer is the most effective solution to oil slick or protein layer formation. There are two types of surface skimmers available in the market.

The self-driven ones utilize electric power and suck all sorts of surface scum into them. 

The working principle of the second type is pretty simple. You have to attach the skimmer with the inflow of a filter.

When the filter draws water into it, the skimmer will guide all floating substances from the surface to the filter’s inlet. Thus the filter will absorb all the fatty matter to deliver clear water.

3) Have an effective chemical filtration

Carbon media can absorb organic fatty matter. If you can have an effective multistage filter with chemical filtration, the probability of this sort of problem is less. 

Even if you use a non-electrical type surface skimmer to attach with the filter, your filter has to have to capability to filter out these oily scums. 

Fish tank with air bubbles inside
Fish tank with air bubbles inside

4) Manual removal with paper towels

In complex aquascaping aquariums, it may not be possible to maintain a powerful water flow. Or, for any reason, you cannot use a surface skimmer.

So, you have a solution to remove the white layer of matter from the top of the water manually by using paper towels.

First, you have to let the surface layer settle by turning off the filter and pump. Then gently put the paper towel on top of the layer to soak it and then pick it right back up.

The protein film will stick to the paper towel and be removed. Take another paper towel and repeat the step for another part of the surface.

Thus you can completely remove the white layer from the top of the water. But this solution is temporary, and the layer will form again.

So, you have to repeatedly do this task in a routine or think about system improvement, as I discussed before.

A Quick Comparison Among The Ways Of Removing White Film

Ways To Remove White Film Performance Suitable For Cost
Air Pump With An Airstone Effective & Cheap Fish that can tolerate high current 10~70$
Surface Skimmer Best in effectiveness All aquarium 30~300$
Effective Chemical Filter Effective but need regular replacement of carbon media All aquarium 7~10$ (Only media)
Manual Removal With Paper Towels Effective but temporary solution Small aquarium 8~16$

Final words

Frankly speaking, I haven’t faced such a problem throughout my entire fishkeeping journey. If you keep all the basics right, you won’t have to suffer. Follow my tips, and I believe that will help you.

Lastly, if you have any better experience fighting against the white film on top of aquarium water, I would love to hear about it. Please don’t hesitate to put your comment in the below box.

Sujit Modak

1 thought on “White Film on Top of Aquarium Water [4 Easy Solutions]”

  1. i have a 5 gallon tank that does not have fish in it. it has a film on top of the water why is that happening. i have other tanks and i do not have that problem.


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