I made this model for myself. I found a few diffuser here but no one was very good for my aquarium. 

In the picture is mine print. There is 2 different colors because the blue was out of stock so I had to change it.

It was printed with A1 mini so other printers can print it.

In the water: 157mm x 100mm x 50mm
The other side of the glass, the holder part:

50mm x 100mm

You can edit the glass thickness. I suggest add +0.2 to your glass thickness.