You may notice from time to time that the surface of your aquarium water builds up an oily-looking film. This is common. This is especially common in aquariums with minimal surface agitation.
If you have no water current at the surface of your aquarium, the water will just sit there. It won’t circulate. Think of the surface of a lake on a sunny day with no wind in the air. The surface of the water is smooth and glossy. You don’t want that in your aquarium under most circumstances.
I notice that when I don’t have good surface agitation in my aquarium that algae and other wastes build up more quickly. The water filtration can’t process the stuff on the surface of the water, so it just stays there. Yuck.
How to add better surface agitation
“Agitating” the surface of the water in your aquarium is easy. Just get a couple power heads (one will do fine if your aquarium is smaller) and set them up so that they create current at the surface of your aquarium water. You should see ripples in the surface of your water.
You will want to keep an eye on the surface of the water for a few days after adding some powerheads for agitation. You may find that you don’t need quite as much surface agitation, or you may find that you need more! Let your eyes be the judge. If you still have oily stuff at the top of your water, you might need more agitation.
Other nice side effects of surface agitation
In addition to now keeping the surface of your water clear through means of agitation, you’ll also add a nice shimmer effect as the the aquarium light passes through the rippling water surface. Cool stuff! Rippling water surfaces can create really nice lighting effects with LED moonlights as well.