When taking a shower the hot water turns slightly to cold and then back to hot water, sometimes two or three times. Is this some kind a build up in the tank or is the water heater. Its about nine years old.

Sounds like a broken or deteriorated dip tube.

Here is a web site on how to replace.
How to Replace the Dip Tube in your Electric Hot Water Heater | eHow.com (http://www.ehow.com/how_5008950_replace-electric-hot-water-heater.html)

Sounds like a broken or deteriorated dip tube.

Here is a web site on how to replace.
How to Replace the Dip Tube in your Electric Hot Water Heater | eHow.com (http://www.ehow.com/how_5008950_replace-electric-hot-water-heater.html)
Im sorry gentleman, I guess I should have said that it was a gas water heater. Am a newbee here and Ill heed the info on the plumbing page.
Thanks
Doug

Symptoms and correction the same for gas.

What's the brand name of your shower valve? Is it temperature controlled? Are your showers long enough for the water to reheat several times in the heater? As you draw hot water out of the top of your heater fresh cold water replaces it. The dip tube directs the cold water to the bottom of the tank where it will be heated and raise to the top.
With a broken dip tube,(see image)the cold water enters the top and mixes with the hot water cooling it down. However the fact that it happens two or three times durning a shower bothers me. This could also be a faulty temperature control in the shower valve.; Do this. Run the hot water out of a different faucet and tell me it it does it there as well. Back to you, Tom