4200L indoor pond in make!

[Jakob]

I will soon start to build my 4200L indoor pond. I have some questions.
It will actually just be a grid made of 2x4s with a plastic (dont know the english word for it).

I will cover the sides of 2x4s with plywood, both inside and outside of the box, to make it look good and for being extra safe. How thick should the plywood be?
Here can you see an unfinished sketchup photo.

 

[Knowdafish]

Length, width, height dimensions? I would use 3/4" plywood and put foam insulation between each wood upright.

 

[Jakob]

300x200x70cm. I have decided to use 1.2cm or 1.5cm.