Options....... remove tank, replace relief valve, remove heater element and try to wash out the corrosion/crystals. How long will it continue to function not knowing the depth of the corrosion before it springs a leak? Another thing I found out is you can buy an OPTIONAL magnesium sacrificial anode that would protect the tank form corrosion

Looking at new tanks it does say this in the literature. "To protect against galvanic corrosion and extend tank life, use of a magnesium anode is highly recommended."

Bottom line is if you have a drain valve you most likely do not have an anode as the optional anode replaces the drain valve which requires removal to empty the tank since you no longer have a drain valve. Did find this though that has a valve built into the anode http://www.suremarineservice.com/Galley ... 1496661821 Will modify it by removing the petcock (valve) and replacing with a 1/4 turn ball valve and hose barb fitting so I can drain to shower sump like it was set up from the factory.
After 11 years of service I decided it is a good time to replace the tank and get an anode for long term protection being I have all winter to shop for a great deal.
