I did a quick google search for aquarium chillers, and found a pretty wide variety of results.
So, what is it that you have? Is this a unit that is supposed to draw water out of your aquarium, cool it down with refrigeration/peltier/radiator, and dump it back into the aquarium? How cold is it supposed to keep the aquarium?
Pics would rock. Also, how were you intending to use it?
Just as an example, if I had a device that was designed to cool down a bunch of water rapidly, and a pump going in and out, rather that worry about cleaning the thing, and worry about it not being able to handle 212 F intake water, I'd hook it up to my immersion chiller (probably need to use a bucket as an overflow tank).
This way, the water going into the aquarium chiller should start off being warm, not 200 F. It should come out of the chiller cold, go through my IC, and
be dumped into the overflow tank hot. Since this hot water is going to mix with the water in the overflow tank, controlling the volume of the overflow tank should allow you to keep the intake water to the chiller in a 'reasonable' range. And as the wort is cooled down, the water coming out of the IC is going to be cooler, and assuming the chiller is designed to get the aquarium to well below room temp, the water coming out of it should be really cold (I'm hoping 40 F) so the IC will keep working well (as they start to become less effective as the temperature difference goes down).
Or, if the thing is really worth a few hundred dollars, maybe you should sell it. You may find you can build a really good chiller that meets your brewing needs for less than the aquarium chiller is worth.