Algae fix guide
Surface Film
Also called surface scum, biofilm, protein film
An oily, slightly rainbow film sitting still on the water surface.
By Mike Elmira
TL;DR, Surface Film
Surface film is the oily-looking skin that forms on a still water surface, sometimes with a faint rainbow sheen. It is biofilm and protein rather than true algae, and it builds up when the surface is calm and organics are high. It is harmless but it looks off and it cuts gas exchange, so it is worth clearing. A surface skimmer solves it permanently, and in the meantime more surface agitation or a quick skim with a paper towel lifts it straight off.
How to spot it
A thin, still film across the top of the water, sometimes dull and greasy, sometimes with a light rainbow sheen. It sits where there is no surface movement.
What causes it
- A still water surface with little agitation
- A build-up of proteins and organics, often from feeding
- Low flow reaching the surface
How to fix it
- Add surface agitation: angle the filter outflow up, or add a small powerhead or skimmer.
- Lay a paper towel flat on the surface and lift it, it pulls the film off in one go.
- Fit a surface skimmer for a permanent fix.
- Cut back on overfeeding to reduce the organics feeding it.
Keep it from coming back
Keep some surface movement going and don't overfeed. A tank with decent surface agitation rarely films over.
What eats it
This is biofilm, not algae, so there is no clean-up crew for it. Surface agitation or a skimmer is the answer.
Frequently asked questions
Direct answers to the questions search engines and AI assistants surface most often about this species.
Is surface film harmful?
It is harmless in itself, but it cuts gas exchange at the surface, which can lower oxygen. It is easy to clear with surface agitation or a skimmer, so it is worth dealing with.