Oil on surface of water...?

[Mordachai]

What the blazes causes that? My water went from crystal to having a rainbow colored skein of what I assume is an oil based substance on it after running for about a week from a rebuild (planted, fish, thoroughly cycled).

I did a 25% WC focused on skimming that oil off the surface, which lasted all of about a day. Now it's back. Makes the lights reflect a rainbow pattern when viewed from below (though the water).

I've looked at skimmers before - but they all seem to be pretty lame (poor quality, easy to break, wrong connectors, float mechanisms seem to work intermittently, etc.)

ideas?...

 

[reefdiver]

Try a bubbler. From what I've read it may be oil from hands and food. I've had luck with the bubble breaking it up.

 

[Mumma.of.two]

Excess organics can cause it. You can try laying paper towels over the surface briefly to remove it. It's harmless.

 

[Tetra1990]

I sometimes get an oil slick after I feed my big tank. It doesn't last long but it's kind of an eye sore.

 

[Fishfur]

I've noticed this only on tanks that don't have anything breaking the water surface. So a nice selection of floating plants will prevent it, air stones help, any filter flow that hits the water helps too.
Paper towel will remove it briefly but it will return if you have nothing to stop it. I see it often on shrimp tanks with slow sponge filters and no floating plants. If for some reason you don't want floating plants, add air stones or adjust a filter so the returning water falls into the water rather than entering under the surface.

 

[Tetra1990]

I've noticed this only on tanks that don't have anything breaking the water surface. So a nice selection of floating plants will prevent it, air stones help, any filter flow that hits the water helps too.
Paper towel will remove it briefly but it will return if you have nothing to stop it. I see it often on shrimp tanks with slow sponge filters and no floating plants. If for some reason you don't want floating plants, add air stones or adjust a filter so the returning water falls into the water rather than entering under the surface.

I have both floating plants, a large mat of water wisteria, and I always keep my water level low just to have surface breakage.

 

[Fishfur]

Same here. I never see that film so long as I have the plants and water falling.

 

[Mordachai]

Thanks for all of the responses. Since it's harmless, I guess I shan't worry about it. For aesthetics, I might look again at skimmers, but low priority.