It was unusable for me on two monitors as the CPU usage was high and never went low as advertised. I eventually got a refund.
Granted my video card is a little dated now, so that may of been the problem. But DX doesn't like multi monitors at the best of times, and the action will tend to only happen on one monitor anyway.
Correct me people if I'm wrong, but I think there may be a new/updated version of Aquarium in the pipeline (). Maybe you should wait?

see link version 2006 is for sale

I liked the look of the 2005 version I built myself with fish and objects available at WC but dropped it after a while because the lighting and shadows for different object were always a little "off" and broke the illusion for me.

I see the same thing in this version. The anchor has a great shadow {as long as you don't want it to lay across other elements - which is understandable} but the treasure chest has none.

I love the fish. I just don't care for the rest.