I had a look in my 2 tanks and I've noticed that there seems to be what I can only describe as a thin oil slick over the surface of the water, this isin both the big tank I'm cycling and my smaller tank.

Any ideas what could cause this? is it harmful to the fish? what can I do to remove it and keep it from happening again? (simple water change or something more drastic?)

Cheers

A cause of oil on the water surface I know of is from your hands and arms in the water. I've never bothered removing it in the past but if you are concerned I think it would take nothing more then a towel spread on the surface of the water/oil. The oil should cling to the towel.

I used to remove oil that way from my old fish pond. The dumb residents of that pond would not eat mosquito larva. So my dads fix for when there were far to many larva and we feared going down the yard. Remove fish, pour in some cooking oil just enough to cover the surface. Then those buggers couldn’t breathe as they can’t swim through oil Muhahaha. It may not have been the most practical way to kill them but that is the type of man my dad is. And it doesn’t harm the fish when you put them back in AFTER removing the oil.

cheers for that, the towel trick worked nicely.

towel? As in, a paper towel surely?

If anybody quotes Airplane now, I'll be dissappointed...

The oil is normal but stops the air getting into the water, directing your filter outlet to break up the surface normally fixes this.

We experienced this recently in a 6ft tank in a cafe. Turned out to be oil from the coffee beans. Added another filter (internal) and problem appears better but still got to go back and check again.

Some years ago I had a similar problem. I used the paper towl method but the problem kept recurring. I finally discovered that the silicone was breaking down. Run you finger along the join and if the silicone feels soft and mushy and comes away on your finger it's time to strip it out and re-silicone. This happened to two tanks which I had re-siliconed 6 months previously, when I checked the tube I had used I discovered it was over 2 years old and probably past it's use by date. A new tube solved the problem.

Regards Gordon

Hi

There is an other way you can get it to go away by ussing a exstantion on you filter (external that is). It works like a offerflo it goos on the end of the water sukking part of your filter it's a fluval part but it can be uset with some adjustment on any type of filter.

scalare

You can get other bands as well, the fluval ones seem to break plus the floating bit that takes in the surface water keep getting sucked underwater.