I have that at my house once in a while.
its a natural occuring thing from the raw water.
hydrogen sulfide is the by product of bacteria that produce hydrogen sulfide during its life cycle.
I have well water, and its much more common in houses that use well water.
It is also common in houses that sit vacant for long periods of time.
the reason your guy told you to change your anode rod was that the anode rod reacts with all the metals of your water heater to keep the elctrons Nuetral to keep down electrolysis and extend the life of your heater. This rod also aids in the production of the hydrogen sulfide by its break down…Or something like that.
chorination of the system is the only remedy, but you can buy different anode rod material that is less reactive and doesnt produce as much by product…But I cant remember if your supposed to change the aluminum rod to magnesium, or visa versa?
Anyway, its not harmful in small amounts, and the human body can smell it WAY before it becomes toxic!
you can add bleach to your heater manually, let it sit, then flush the whole heater or get an aoutomatic chlorinator at the heater, and then add a filter to remove the chlorine AFTER the heater…But I just deal with it and tell my girlfriend that its just my dirty socks that are making the smell!