Overflow Height SpacerEvery tank is slightly different, and that means any protective lid has to be specialized to it. Some tanks have overflow boxes that are lower than the top of the tank glass, meaning that any will bow in the back due to lack of support. Examples of tanks with this style overflow are: Red Sea AquaForest Oceanguard Waterbox Cube and AIO Planet Aquarium Tideline AIO The Top Lids Overflow Height Spacer fixes this issue. Made specifically shaped and sized