Acrylic wall thickness

[Delphinus]

Question for you acrylic fabrication gurus.

Is 4.5mm wall thickness adequate to hold 20g of water in say, (roughly speaking) 24x12x20 dimensions?

What about 40gallons, but partitioned into 2x20g compartments?

And just to be really crazy, what about 60g of water in 3x20g compartments?

Note that not all compartments will necessarily be filled with water simultaneously. I'm toying with an idea of some two larger surge tanks for the reef, flanking a refugium in the center. So the centre compartment would probably be filled full-time, but the side compartments would be fill-flush-fill-flush-etc.

Would 4.5mm acrylic be sufficient or should something like that be built out of thicker acrylic (6mm/.25", or even larger perhaps??)