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Finding a white oily film on the surface of your aquarium water isn’t unusual. But you’ll want to know what caused it. And you’ll want to now how do you get rid of it. Luckily it’s not difficult to remedy.
A white oily film can develop on the surface of aquarium water for several reasons. The most common causes are listed below.
- Your Hands
- Food Quality
- Overfeeding
- Poop
- Tank Position
- No Lid On Tank
- Lack Of Surface Agitation
- Dead Zones/Low Flow
- Dead Fish/Tank Inhabitants
- New Filter/Equipment
- How To Remove Film From An Aquarium/Tank
I’ll cover each cause on the list above followed by the solution(s) to help you get rid of your surface film. Plus there’s some general tips for avoiding the issue.
Keep reading for more information and tips
Your Hands
Fish/Aquarium keepers have their hands in tank water regularly. In fact we’re often up to our armpits in aquarium water! Getting wet is part of the aquarium hobby no matter which aquatic creatures we keep.
The thing about human skin is that it naturally secretes oils. And on top of that we use personal hygiene products to keep our skin in good condition. A combination of these things can make us a little greasy when it comes to tank maintenance.
This means that we’re likely to be the biggest cause of oily film in our tanks.
Solution:
Wash and Rinse your hands thoroughly before putting them into your tank. If you’ve got a larger tank, or you’re going to be reaching down to the bottom, you need to make sure you’re arms are oil/soap free too.
Rinsing off is really important. You don’t want any unexpected chemicals going into your tank water.
It’s a good idea to keep some aquarium-safe gloves (Amazon link) ready for emergency situations. Because you never know when you’ll need to get your hands into the water quickly to sort out a problem. They’re also useful for general tank maintenance too.
Food Quality
Always buy the best quality food that you can afford. Cheaper foods might seem like a bargain at the time but they may cause you problems in the long term. Some cheaper foods contain poor ingredients and additional oils that can mess up your tank water. Plus the lack of nutritional content won’t be good for your tank inhabitants.
Solution:
The simple solution is to buy a reputable brand of food. I know this can be difficult if you’re on a tight budget. But keep a check on offers at your local Pet Store, Aquatic Dealer and Online.
Overfeeding
Overfeeding means that you’ll end up with uneaten food decaying in your aquarium. The decaying food pollutes the water which puts your fish/inhabitants at risk. It also means that you can end up with an oily film on the surface of the water.
Solution:
Don’t overfeed your tank. It can take time and practice to judge how much food is enough. But it’s worth the effort. After all, it will save you a lot of extra work in the long term.
Poop
Anything that an aquatic creature eats is going to come out of the other end on a regular basis. The poop will fall to the bottom of the tank and after a while it will start to breakdown. So you’re going to end up with digested food stuff decaying and releasing toxins, along with other things, into the water column. This can include proteins and oils that cause a film to develop on the water surface.
Solution:
Carry out regular tank maintenance that includes gravel/substrate vacuuming (Amazon link) to remove as much poop as possible. Don’t overdo it though or you will upset the biological balance in the aquarium.
Having live plants that are rooted in the substrate helps too. The plants use up nutrients produced by the poop as a fertilizer. This helps to reduce the amount of toxins etc that are being released into the water. Which, in turn, reduces the chance of a film developing.
Tank Position
The position of your tank can affect the likelihood of a film developing on top of the water. If your tank is in a cooking area, or in a room where you regularly use spray products, you’re more likely to get film on the water.
Solution:
Reposition the tank as far away from your cooking area as possible. If your tank is situated in an area that needs regular use of spray products put it somewhere else. Simply moving your tank to a different position can make all the difference.
No Lid On Tank
lidless tanks are popular in the aquarium hobby and look attractive. They’re also ideal if you prefer to have a hang-on-the-back filter or other aquarium equipment that is designed to hook over the edge of the glass. But an open top tank can add to the problem of film developing on top of the water. The reason for this is that without a cover the water will gather dust particles from the air. And any airborne cooking residue and household spray products will add to the build up of film.
Solution:
There are two main solutions to this problem. You can either add a lid/cover or move the tank to a position less likely to attract things that will cause a build up of film. It’s worth bearing in mind though that whatever position your tank is in dust particles will always land on the water. So adding a lid/cover may be the best option in this case.
Lack Of Surface Agitation
If the surface of the water isn’t constantly moving you’re more likely to find that a film builds up on top of it. Aquarium filters work in different ways. Some move the surface water around quickly and others are more gentle. Gentler surface agitation takes longer to breakdown and disperse any film build up on the top. Which means that an oily film is more visible.
Solution:
You can increase the surface agitation in different ways.
- If you have an adjustable filter (Amazon link) you can increase the flow and surface movement.
- If your filter outlet has a spray bar (Amazon link) you can angle the bar up towards the surface to create more movement. If it doesn’t have a spray bar already fitted you may be able to add one depending on the type of the water return outlet.
- Add an air stone run by an air pump (Amazon links) to create bubbles that rise and increase the surface water agitation.
- Add a wavemaker (Amazon link). Wavemakers move the surface water around at a fast pace. They are often adjustable so that you can control the flow.
Tip: If you need to increase the surface water agitation to reduce surface film you need to keep your tank inhabitants needs in mind. Some aquatic creatures don’t do well with fast water movement. So do some research on them before you speed things up.
Dead Zones/Low Flow
A film on tank water can be caused by ‘dead zones’. Dead zones are areas of an aquarium that get little or no water flow. Even if you have enough surface agitation there could still be dead zones lower down in your tank. If there’s not enough space for the water to circulate freely between plants and tank decorations dead zones can develop.
Solution:
Thin out your plants with a little trimming and space out your tank decorations. Making more room for the water to flow freely throughout your tank will help to get rid of any dead zones. Which, in turn, helps to reduce the build up of surface film.
Dead Fish/Tank Inhabitants
When a fish or any other tank inhabitant dies it starts to decompose. During decomposition the ‘body’ releases a lot of different substances into the water. And these substances include things that can cause an oily surface film to develop.
Solution:
Remove any dead fish etc as soon as you see them. Even if the other tank inhabitants are feeding off their dead tankmate it’s still best to remove the deceased as soon as you spot it. This helps to reduce any dangerous or oily substances being released into the water column.
New Filter/Equipment
New filters and aquarium equipment tend to come with some dust/debris and often oil from the manufacturing process. So if the film on your tank water started after adding new equipment this could be the cause.
Solution:
Preferably thoroughly clean any new tank equipment before you add it to the tank. If you’ve already added it and you’re having a problem with a film developing remove the new equipment, give it a clean, then add it back to the tank. You may still have to remove film for a while until it’s all cleared. But if the new equipment has been cleaned it won’t be such a long job.
How To Remove Film From An Aquarium/Tank
Although tank film is a nuisance it’s not too difficult to remove. Here’s some simple ways to get rid it.
- Paper Towels – Lay some paper towels on the surface of the water. Give it a few seconds to let the film stick to them. Then carefully remove the paper towels. You’ll probably have to repeat this a few times until you’re happy that you’ve removed at least most of the film.
- Use A Plastic/Disposable Cup – You can use a beaker/plastic cup to skim off the film. Gently submerge the cup with the bottom pointing down into the water at a slight angle. Slowly use the cup to skim off the surface film/scum emptying it after each sweep.
- Install A Surface Skimmer – There are aquarium surface skimmers (Amazon link) available in different styles and capacities depending on what you need for your tank. Surface skimmers are designed to remove film and debris from the water’s surface and some are also designed to increase water flow. They’re worth taking a look at if you have a recurring problem with surface film despite your best efforts.
Is An Oily Surface Film Dangerous?
Generally speaking a little bit of surface film on a tank/aquarium isn’t considered dangerous. However, if the film is dense and totally covers the surface area of the water it can cause serious problems. The biggest problem is that it can prevent the gas exchange process in an aquarium. Which means that toxic gasses can’t escape and oxygen can’t get in. A thick film can also reduce the amount of light that reaches live plants and they may suffer.