LOL, Carol, I used some that I got from Greg. It was between 1/4 and 3/8. It was really old. It took me several hrs to get the paper off. I ended up putting some strips af acrylic vertical to on the side to hold the ends and put a horizontal brace about 1-1/2 down from the top to keep it from bowing. It worked out good and I got the sand and water back in last. I built a PVC rack for one of the rock islands last night. I am about to head to Lowes for eggcrate to attach to the rack now. Hopefully I will be able to put some rock in the tank today.