Currently using 3 different methods to black out a tank.*
1. Aquarium backgrounds. It slides nicely between the glass and the black framing. Some parts are taped using scotch tape.
2. Black construction paper using masking tape.
3. Black wrapping paper using masking tape.
I wanted to see which would work better for over all durability, price, aesthetics, and ease to put on. So far I think my favorite is the black construction paper. All suggestions listed have bee useful imo.
*All tape and black out material is on the outside of the tank.