I have the light diffuser from HD aka egg crates and I have it on the top of my 55, my diamond goby jumped a couple nights ago for the 3rd time. He wasn't that small either but definitely fit through the holes in there. You need something with smaller holes like 1/4 size. Check out BRS for the DIY screen top. Just use the egg crates for the back of the tank if you have a return, HOB
skimmer etc. that's what I'm going now. I caught him in time the first 2 times he jumped... not the 3rd.