I have two different aquarium screen savers. The "XP Plus" one will only do one screen and the other one goes black. The other one is called "dream aquarium" and it does both and has a ton of features. I used to have the Dream aquarium go on after 15 mins and lock my PC. A few times I got up in the middle of the night and my PC was really revving... figured it was because of all the 3d scaling ect... (I keep my PC on 24/7).
Now I just use the starfield.
Had a cat. She would sit for hours and watch my fish (on her but, whole body stiff and head going back and forth...). LOL
First attachment is plus (freshwater), second is plus (marine)...