Green scum on top of tank under light not in the water

[hdsparky]

This green scum is under the light on top of tank,not inside. Should I get new bulb?

 

[Byron]

I am assuming you mean that the green scum is on the glass that separates the light tube/bulb from the surface of the water. The cover glass, especially the portion under the lighting, should be removed and cleaned (both sides) at every weekly water change. This will prevent a buildup of minerals (from the water that condenses and then evaporates from the cover glass every day/night) and algae.

Do you have live plants? If yes, then the light is important as it will reduce intensity the longer you have it, and regular replacement (before it "burns out" on its own) is necessary. Without live plants, there is no concern over this.

Byron.