Black background for back of tank

okay so today I put a black background one the back of my tank and also on one of the smaller sides that faces a wall. (in other words the corner) and now my fish seem unhappy -- is this a bad sign? should I remove background or will they adjust?

Blank Tank Top Color Black Front and Back View on White Background Stock Photo - Image of male, clothing: 203908090

black background

Womens Black Tank Top Vector Template Stock Vector (Royalty Free) 1597574860

Young woman on white background sitting leaning back full body in black Tank top Stock Photo

Blank womens black tank top in front, back and side views. Realistic female sport shirts Stock Vector by ©kololo15 274860334

Blank tank top color white and black front view on white background Stock Photo

Trying to decide if a black background or no background looks better. Any thoughts? : r/PlantedTank

The blackwater tank, currently cycling. Got to get a black background set up! : r/Aquariums

HOW TO: paint an aquarium background