Anyone know why my goldfish tank has steamed up above the water level?

[CADS]

Hi

We have a goldfish tank with a lid but it has steamed up above the water level. Is this normal? Our water filter is set to half way between minimum and maximum.

Any ideas? They are ds's goldfish so we don't want them dying on us.

Thanks

dose it happen when the light is turnd on? maybe it is eveaperation?

or sunlight on it?

It is either normal evaporation/condensation, or is the filter bubbling above the surface and splashing? What type of filter is it - one with an external air pump or an internal filter?