Nope, not the leveler bar, it's the top of the filter between the return lip and the body that isn't wide enough. Most likely because it's not made for a tank that big? Fits fine on an old 20 gallon I've got. I was only putting it on the 125 gallon to get the bacteria colonized before starting up a 29 gallon, which is where it'll end up. I just took the bio-media from the AC
and stuck it in the sump of the 125, hopefully that'll get the bacteria growing.