So the propane company tried to get the tank up to standards by installing an insulated pigtail pipe that insulates the tank from the propane piping. But still did not pass. So they came back and installed the bag of sacrificial anodes and now it easily passes. Cost to install the bag of sacrificial anodes & test was $390. I was quoted $250 (plus shipping) for a bag of sacrificial anodes alone. I can also get the special probe for $50 and use a voltmeter to test myself.
The lingering question is how much corrosion has occured during the time between when the sacrificial anodes were fully sacrificed (gone) and now. One assumes since the tank was initially rented that the propane company that installed it in 2000 would have included a bag of sacrificial anodes since they rented the tank and would have wanted it to last as long as possible.