Lesson learned here-never fit 3D background by wedging it in..

[cichlidfish]

My first go-around with a diy background I made, I had the same problem. I am planning on installing a 3-piece diy background I bought on ebay on one of my tanks soon, and will be silicon-sealing them in place.

I have a 25g where I did it right with the silicon sealing, and no issues.

 

[jhook]

I've got one by Universal Rocks. Looks awesome, but I scratched my glass front trying to get it in place. That sucks. Also, since I didn't silicone it in place it kind of floats about an inch off of the bottom glass so small fish get behind and go back and forth. Not too bad since my HOB overflow is back there. It allows for free flow of the water.