I can't even tell that was foam! I was thinking how heavy that background was because I thought it was all real rock! You’re going to have to answer a few questions about that background

1) Did you individually coat each foam block with cement then install the foam blocks to the back of the tank?
2) How did you glue the foam to the tank? Was that area not covered with cement then just silicone to the tank walls?
3) Did you have to tip the tank on its back to get everything glues and sealed?
4) I will have more questions depending on these answers
More pictures! This background is awesome!