What is the Oily Film on Pond Surface? {3 Removal Tips}

Are you seeing or noticing oily film on your pond surface? Do you know what is the oily film on pond surface?

What effect does it have on pond life? Do you know how to get rid of this oily film?

This article contains details about the oily film and how to eliminate them from your pond surface.

What is the Oily Film on Pond Surface?

The oily film is known as biofilm which occurs when microorganisms stick to the surface of objects in the pond while they begin to reproduce.

They form an attachment by secreting slimy, glue-like substances, which causes the biofilm at the pond’s surface.

The best way to remove the oily film from your pond is to treat the water with beneficial bacteria which you can get on Amazon.

Oily Film Pond Surface

Why Does My Pond Water Surface Look Oily?

You can mistake the oily film on the surface of your pond water for an oil spill or algae bloom. But you are mostly on the wrong hook as the most common cause of the oily film is bacteria.

1. Do Bacteria Live in Ponds?

Yes. Bacteria, archaea, viruses, protozoa, helminths, and protists are among the microbial species that are naturally present in ponds. The majority of these bacteria are essential to each system’s ecology and helpful.

  1. The action of bacteria in the pond can cause the water to develop oily film at the surface.
  2. The oily film occurs when there is a large amount of animal life or decaying plant in the pond in bacteria presence.

2. What Causes Biofilm?

You can classify the films as a dead protozoan or algae scums.

  • Biofilm can also occur when these microorganisms produce slimy, glue-like substances when they are reproducing.
  • Biofilms are a good sign that your pond is of low water quality and out of balance.
  • The cause of biofilms in the pond is dissolved organic carbon.
  • It forms when metazoan or algae life dies faster than naturally occurring bacteria can degrade it.

Dissolved organic substances support biofilm development and reproduction.

How to Remove Oily Film on Pond Surface

The oily film on the surface of your pond might not be harmful to aquatic life, but prolonged cases can make it harmful. You can remove the oily film from the surface of your pond in several ways.

1. Beneficial Bacteria

The best way to remove the oily film from your pond is to treat the water with beneficial bacteria which you can get on Amazon. 

You can also add beneficial bacteria to the pond. These beneficial bacteria will help you eliminate the cause of the oily films in your tank. You can also add bacteria or enzyme products to the pond to get rid of the oily film.

2. Raise pH

You can also raise the pH level by adding lime to the pond. It will serve as good control of oily films. An ethical solution to biofilms in your pond is to keep good water quality.

One way you can remove the oily film is by raising the water’s pH. Raising the water’s pH will cause the film to disappear as it will ensure protozoan and algae life are minimal in the tank. You can raise your pond water’s pH level by adding soda ash.

3. Water Changes

When you notice oily films sufficing at the surface of your pond water, you should start changing the water regularly. You can also use a water filter and water pump to ensure good water quality. When you see the oily films on the surface of your pond water, you should know the water is of reduced quality.

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How to Prevent Oily Film on Pond Surface

The sole cause of oily film on your pond surface is poor water quality. The microorganisms that cause the oily film would not be in the pond if the pond water were of good quality. To prevent this oily film from the surface of your tank, you have to make sure:

  • you maintain adequate water quality.
  • the water’s pH is at the right level. Improper pH values will make the water conducive for them.
  • the water is of the right temperature as an inadequate temperature will support the microorganisms’ existence.
  • you perform a regular water change to ensure the water is always clean. 
  • to use water filters, pumps, and other necessary devices to keep your water quality intact.

If you can maintain good water quality in your pond, you will prevent this oily film.

Will Oily Film on Pond Surface Harm My Fish?

The type or cause of the oily film on the surface of your pond will determine if it will harm your fish or any aquatic life. If the oily film results from oil spills, it can be detrimental to your fish.

  • It will trap and prevent the exchange of gases in the water, causing limited oxygen for your fish.

This kind of oily film will trap gases for your fish and pose a risk of toxicity. The oil spill contains chemicals that can be very harmful to your fish. These chemicals will kill your fish and every aquatic life faster than suffocation.

If the oily film results from microorganisms’ activities, it is a bit less harmful but not completely safe for your fish. It will also trap gases, but it will provide little or no toxicity.

How Do You Remove Biofilm from a Pond Surface?

The main cause of biofilm is poor water quality. If you can maintain adequate water quality, you will remove the biofilm. You can also raise the water’s pH and treat it with bacteria and enzyme products.

You can also use herbicides and algaecides to remove biofilms, but you have to be careful of excessive usage. Ensure you keep good water quality, and the biofilm will be off in no time.


The oily film on the pond surface is mostly a result of microorganisms in the pond. It can also have other causes, but other causes are rare. Biofilms occur due to poor water quality, so you have to keep good water quality to get rid of it.

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John Brandon

John has kept fish all his life (since he was about 5). He started with keeping guppies and fell in love with fish keeping almost straight away. That was 40 odd years ago. These days John still keeps fish and currently has two large tanks where he keeps many different types of fish such as Angelfish, Neon Tetras, Goldfish, Guppies and many more.