I have a used acrylic tank that I am in the process of setting up and I could use some advice. The tank is drilled in the bottom and the return water comes up through two small towers with holes at the top. At the bottom of the towers it looks like the previous owner cut a slot in in each one. The left ower is partially covered (damaged?) and the other is wide open. I would like to permanently close these cuts so that all of the water returns through the top of the tower but I am not sure how to do this. The surface is triangular with the point being rounded. I could glue two pieces on each side of the triangle but that wouldn't close the cut right in the middle. Any ideas how to fix this?