Generated heat is the dreaded enemy of your system components. The harder you run your video card, the more heat it produces. Speaking from past experience, ( of course I had mine overclocked at the time as well ), running one flat out for hours on end CAN fry the card. I've had it happen.
Basically what you want to try and do is watch the aquarium and turn your sleep settings up so that your fps is down as low as you can get them, and still maintain smooth movement. That way you still get the great look of the aquarium without endangering any of your components needlessly.
