Water treatment dealers deal with this all the time.
Obviously you have some sulfate in the water and some sulfate reducing bacteria (nonharmful). Turn the temp up to 140f or remove the magnesium anode rod (voids waranty) or replace it with an aluminum rod.
You should drain and flush the tanks and then sanitize them. You can find out how to do that by searching ither the web or newsgroups at http://www.google.com.
Quality Water Associates