How big should a sump be for an AIO?

[grrrrhh]

It's my first time owning an aio. I got a cube 12g custom made and the sump seems to be too big. Upon measuring, the sump takes 4g out of the 12. Is this okay?

 

[Gtinnel]

In my 15g AIO the filter area takes about 3.5g so that seems pretty standard.

 

[grrrrhh]

In my 15g AIO the filter area takes about 3.5g so that seems pretty standard.

what return pump do you use for that 15g?

 

[Gtinnel]

what return pump do you use for that 15g?

I use a little pump from IOAOI. They had a trial thread for the pump so I ultimately got it for free. It does a good job but I run it on full speed, so ultimately it’s as small as I would want use. It’s still decently bigger than the pump that was free with the tank.
Amazon product ASIN B09P2XLRPL