How to make the background Pitch Black like this?

This is an ad from Waterbox. Also in many other tanks I've seen they have a pitch black background, meaning little to no light reflection on it. In my 75gal tank I struggle to do that. My Kessil lights always spill some lights on the background.

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how do i make only the object light out in a pitch black background like this pic right here? : r/blenderhelp

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how do i make only the object light out in a pitch black background like this pic right here? : r/blenderhelp

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