So what happens if you start to get a weird scum on the surface of your tank water? Before you can fix the problem, it helps to know the cause.
An oily film on the surface of the water could come from:
- Oily fish food. Some frozen fish foods are very oily, and can leave a residue on the water’s surface. Changing fish food brands may make a big difference!
- Oily people food. If you do a lot of deep frying, there may be oily vapors settling on the surface of your aquarium water. Keeping your tank securely covered can help prevent this kind of film.
A colored film on the surface of the water could be algae. Algae is tough to deal with, because if you miss a tiny bit in your clean-up, the algae can come back. Changing the tank lighting or the water chemistry may be your best bet — it will hopefully make the tank less hospitable to the algae.
A milky, bubbly scum could actually be a bubble nest! Some types of fish — particularly bettas and gourami — build mucousy bubble nests. It may not be “scum” at all.
If none of these possibilities solve your problem — and there are lots of other reasons for surface scum in your aquarium — don’t give up hope. Increasing surface agitation or changing the water flow in your tank can clear up your dirty little problem. Basically, if the water is in motion, particles will be less likely to clump together. Agitation also increases oxygen levels in the water, and may help encourage bacteria in the water to do some clean-up work.
If all else fails? Try placing a paper towel sheet on the top of the water. It may just soak up the filmy mess!