Wow! That has got to be the best betta tank ever! I think it looks like a 10 gallon, amazing work with details. I made a foam background twice, if you use plenty of glue then the wall won't float up. The biggest problems I ran into was the foam rocks loved to detach and fly out of the tank like rockets! You might want to look into using liquid nails and crazy glue also, having the background fall apart is no fun. Can't wait to see this tank planted up! Oh yeah, vinegar might help the cement cure a little quicker, just Google around, some good tips/tricks out there!