[feldon34]

The ideal Sleep setting is the highest number, while the animation of the fish and the Aquarium are still smooth.

When Sleep is set to 0, your computer is working as hard as it possibly can to generate frames of animation, possibly generating hundreds of frames of animation you don't even see.

By increasing the Sleep amount, you are 'giving your computer a break' and allowing it to generate less frames of animation. If, with a setting of 10, you still have smooth animation, then that's where I would leave it.

If you press the "S" key, you can bring up a display in the upper left corner that shows you several pieces of information including the number of frames per second of animation being produced. If that number is over 40, you'll typically have smooth animation. Press the "S" key again to hide this data readout.