Aquarium backgrounds give some oomph to your setup, making your tank look bigger and fuller, without taking up valuable space. You can add a backdrop on the outside of your tank at any time, whether the tank is full or empty. But if you prefer to place the image on the inside of the tank, it'll take some work.

Can you put aquarium background inside?

You just need to slide the background inside your aquarium. You can have water in your fish tank and even fish and other decoration. It's recommended to drain some water to avoid spillage during sliding the background inside your tank. You can squeeze the background inside the substrate, so it will support it.

Do terrarium clings go inside or outside?

It's best to put it on the outside. You will probably have to trim it a little as it is true size to the outside dimensions of the total W/H/D of the terrarium.