How to Clean the Scum Off the Top of the Aquarium

Lay a paper towel flat over the oily water surface, holding the edge of the paper towel with your fingers. Let the paper towel soak up the water and scum for a few seconds, and then peel it back and up, like you would for a sticker. If the nasty scum still remains, repeat with new paper towels until the oil is all gone.

Opt for the cup method. Lower a cup into your tank until the water starts trickling over the lip of and inside the cup. Follow the scum along the surface, keeping your cup barely below the water so that most of what filters into your cup is the film. Keep a bucket next to you so you can dump out the water occasionally.

Remove the scum with a plastic baster. Long thought of as cooking tools, basters are also useful for your aquarium. They're often used to feed your fish certain meals, such as brine shrimp and bloodworms, and to target-feed specific fish, but they can also suck up the film along the surface of your tank. Dip the baster a smidgen into the scum. Squeeze the rubber bulb to pull the water and scum into your baster. Squirt the yucky stuff into a bucket.

Add a protein skimmer if you have a saltwater tank or a surface skimmer if you have a freshwater setup. Protein skimmers are much more effective than surface skimmers, but they typically only work in a saltwater tank. A surface skimmer removes organic waste at the surface of your tank, while a protein skimmer removes organic waste throughout your tank. Both help improve water quality and should cut down or completely eliminate the film that forms at your tank's surface. Surface skimmers work in saltwater tanks, but most saltwater setups run more efficiently with a protein skimmer.

Increase surface agitation. Increasing surface agitation disturbs the film and often prevents it from forming. To increase surface agitation, trim plants that have grown close to or obstruct your filter outflow, add a more powerful filter to your tank or add a powerhead, which is a device that pulls water in and spits it back out to increase water flow. If you have a hang-on-the-back filter, try lowering your water level slightly so that when the water flows out of your filter, it makes a splash on the surface. Skimmers also increase surface agitation.