I had the same problem due to high iron content. Whenever it gets
heated up, whether you have gas,oil, or electric water heater, it will
"agitate" the iron and cause some kind of chemical reaction.
The way my water company advised me to flush it was to first turn my
gas control to pilot( in your case it would be just shut off the
breaker). Then attach a garden hose to the drain at the bottom. Run the
hose to a nearby sink or drain, then open the valve and let the water
run continuosly until it runs clear, which might take 10 minutes.