Thanks for the link. A friend was told to just use antifreeze instead by the prepackaged stuff so I was wondering if anyone had tried it.
I suppose that you could use antifreeze in the cooling loop, but unless your rig gets that hot or is exposed to freezing temperatures, it doesn't make much sense. Antifreeze does three things: it lowers the freezing point, it raises the boiling point, and it provides some corrosion resistance, especially for engines with iron blocks/water jackets and aluminum radiators. If you're just cooling the CPU, you should never get near 100 C, so the boiling point is not a problem. Likewise, you'll probably never freeze your computer, either. Corrosion may or may not be an issue, but a very slight mixture of antifreeze to water (10-15%% Et(OH)2 to 85-90% H2O) is enough to halt corrosion. Now a GPU can create some serious heat, so perhaps a stronger solution is needed. A regular 50/50 mix will not boil until about 130-140 C, so figure in the temp of your GPU and add 20 C or so for safety, mix accordingly. There usually is a table on the side of the antifreeze jug.
The big issue in water-cooled systems is leakage. Water with antifreeze dissolved in it is a very good conductor and will trash your system if it leaks. Mainframes and data centers that use liquid cooling generally use a nonconductive coolant liquid like Fluorinert instead of water. Electrical transformers are cooled with a similar liquid. I'd suggest this stuff over water if it were my box, although I haven't tried to find any of it.