My fish tanks always stay at a constant temp. of 72 F. How can I lower the temp. of the water?

usually, a water change will lower the temp. why do you want to lower the temp in the water?

I think 72 is a good temp. That is where mine usually is. Remember don't change it drastically for whatever reason you are lowering it.

I want to lower the temp. b/c most of the books that I have read stated that goldfish prefer temp. around 64-68 degrees. So, 72 degrees is a good temp. for goldfish?

Yep. The biggest thing about the temp is you want it pretty stable. It shouldn't go up and down alot. And you don't want it too warm (like in the 80s). They are cold water fish but they have a little range you can fall in.

I did a search for water temp on the boards. Here is a article about keeping goldfish you can read. It says a good temp is up to 75.
If your tank has been at 72 the fish have adapted to that and should be fine.

http://www.kokosgoldfish.invisionzone.com/...ter+temperature

10. THERMOMETER. A tank thermometer is very useful, especially if you live somewhere that has very hot summers or very cold winters. Goldfish prefer a temperature of between 65F and 75F. Below 50F they will go into a form of hibernation and above 85F they will begin to suffer.

Sorry David ,but if you're doing water changes,and your temps are lower because of that , may mean that you may be doing them incorrectly. Lower/higher temps added to your goldfish tank is one of the reasons fish get Ick & other health problems.Goldfish and any other fish need to have near matched temps when water is added. Elanas your temps are stable and they are fine.