Marine Aquarium 2 MD (Multi-Display) works on multiple independant monitors. You may need to press the SPACE bar to bring up Settings and make sure each display is not set to [X] Blank. In my opinion, MA2MD should ask at startup on the first time
You seem to have more than one display connected to your computer.
(Run the Aquarium on the Primary Display)
(Run the Aquarium on All Displays)
(Advanced Settings)