How often do I need to change my liquid coolant?

Not sure of the specified times, six months to a year is what I have seen spouted by other water cooling gurus. As for neglecting it, it's not advisable. Your water loop will start to grow algae which will coat the inside of your water block(s) and radiator. Think of algae like dust on a heatsink. This will hamper direct heat transfer from the block(s) to the liquid and the liquid to the radiator. As I hear it, it is also very hard to remove once it's there, especially from the radiator.

So my advice would be to drain your loop if you are somewhere in the timespan I have said and flush it through with clean distilled water and drain it again. Then refill it and add new additive. You may also want to wait for confirmation from someone who actually uses water cooling though, since I am only going off what I have read.

Here is a link with some instructions:

http://www.maximumpc.com/article/h [...] ling_setup

Here's another:

http://www.custompc.co.uk/howtos/w [...] page1.html

I drain, fill run for an hour or so, drain and fill. Thats good for every 6 months. The next 6 months I do this:

Cleaning a loop, not a new loop: I do this once a year, I drain and refill at 6 months, the next time I do this……
Wash hands very well, getting rid of hand oils.
For pumps and blocks, fittings, clamps, acrylic res/block parts.... not hose, tear it to smallest pieces, put in a bowl, heat water up not to boiling add 10% vinegar, when hot, pour over parts. Rinse in 10 min or so. Put aside.
The bocks will probably have some black oxidation. Take the copper parts out of the pile of parts you took out of the water. Dry well and pour ketchup on them, and set aside. Only the copper parts need this.
Rad cleaning: fill with very almost boiling hot water. Let sit 10 minutes, drain half out and shake for 5 min. Repeat till liquid is clean.
All the pump, block, fittings, and clamps, inspect, get in the tiniest corners with a tooth brush. Kind of meditative, time consuming, you learn a lot about o-ring size, how it all feels. Run a rag using a coat hanger and dish soap through the tubing, rinse well.
Rinse all the parts and hose with distilled, dry then really dry with an air compressor (nice extra step to get rid of water spots). Don’t need to dry the inside of the hose.
Now on to the copper parts, they should have been soaking an hour or two. A toothbrush and ketchup should clean much of the oxidation. It probably won’t be like new, but pretty darn good. Rinse, dry, and blow the parts.
That’s it.

LOL!

If you follow that link for CustomPC, they suggest using a commercially available cleaner. It will kill algae and remove copper oxide. Have a look.

I'm now running 4.3 Ghz OC on my i7 920 D0. I can't do that with air cooling. If I can find a faster way to clean my loop, then I'll do that instead. Remember: lazyness is the mother of invention.

I'm trying to figure out how being lazy makes you motivated enough to create something else, when it's just as simple to do it the normal way?

You have odd brown stuff growing now? Well your past the rinse and forget stage. Your in for a major job. You have to do it.