Actually two 24 inch x 18 inch above the rim or actual measured inside the rim = 21 1/8 x 16 3/8 hinged tops work perfect - remember- when this is fully functional the one side will only have the plumbing coming out of the side to the external pump. The other side will have the plumbing coming down from the sump above - but I will be rotating/changing the plumbing so that it will flow into the back side of the 75 refugium = where the plastic area is on glass hinged covers - so I can cut them to fit. So, ya please pick them up - I will drive to your place to pick up ASAP. Gives me an excuse to see your setup as well.