My Water Heater is Knocking pretty loud for the last 10-12 months... I'm trying to figure out if this is ready to die and I should replace it before it does. It's 6 years old, new with the house and it's got a 6 year guarantee.

About 6 months ago I drained it. The water was clean, but I refilled it and drained it again and I started getting this blue stuff out of it... It looked kind of like light blue crystals, different sizes but about the size of rock salt.

Someone told me the glass lining of the tank is really fiber glass and that's probably what I was seeing. If that's the case I think I want to change the water heater before it dies and leaks all over... probably on Christmas eve...

It's a 75 gallon tank with a recirculating pump, I keep the heat pretty hot so the hot water lasts longer.

Any ideas? Thanks!